lib: change ' to ' to satisfy Outlook HTML rendering

The HTML entity ' (') did not exist in the HTML 4 spec [1] and was only
added later.
As Outlook (and Thunderbird) uses an old engine to render HTML and CSS, it does
not recognize this entity and treats it as a literal string.

Therefore, use the equivalent ' code which should be recognized by all
browsers, even those restricted to HTML 4.

[1] https://www.w3.org/TR/html4/sgml/entities.html

kallithea/lib/helpers.py

@@ -85,7 +85,7 b' def html_escape(s):'
         .replace(">", ">")
         .replace("<", "&lt;")
         .replace('"', "&quot;")
-        .replace("'", "&apos;")
+        .replace("'", "&#39;") # some mail readers use HTML 4 and doesn't support &apos;
         )
 
 def js(value):

kallithea/tests/models/test_dump_html_mails.ref.html

@@ -94,7 +94,7 b' View Comment: http://comment.org'
     <tr>
         <td width="20px" style="width:20px"></td>
         <td>
-            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &apos;comment&apos;.<br/><br/> - and here it ends indented.</div></div>
+            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &#39;comment&#39;.<br/><br/> - and here it ends indented.</div></div>
         </td>
         <td width="20px" style="width:20px"></td>
     </tr>
@@ -253,7 +253,7 b' View Comment: http://comment.org'
     <tr>
         <td width="20px" style="width:20px"></td>
         <td>
-            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &apos;comment&apos;.<br/><br/> - and here it ends indented.</div></div>
+            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &#39;comment&#39;.<br/><br/> - and here it ends indented.</div></div>
         </td>
         <td width="20px" style="width:20px"></td>
     </tr>
@@ -430,7 +430,7 b' View Comment: http://comment.org'
     <tr>
         <td width="20px" style="width:20px"></td>
         <td>
-            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &apos;comment&apos;.<br/><br/> - and here it ends indented.</div></div>
+            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &#39;comment&#39;.<br/><br/> - and here it ends indented.</div></div>
         </td>
         <td width="20px" style="width:20px"></td>
     </tr>
@@ -607,7 +607,7 b' View Comment: http://comment.org'
     <tr>
         <td width="20px" style="width:20px"></td>
         <td>
-            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &apos;comment&apos;.<br/><br/> - and here it ends indented.</div></div>
+            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &#39;comment&#39;.<br/><br/> - and here it ends indented.</div></div>
         </td>
         <td width="20px" style="width:20px"></td>
     </tr>
@@ -728,7 +728,7 b' Subject: Test Message'
                     <td>
 <table cellpadding="0" cellspacing="0" border="0" width="100%">
     <tr>
-        <td style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the &apos;body&apos; of the &quot;test&quot; message<br/> - nothing interesting here except indentation.</div></td>
+        <td style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the &#39;body&#39; of the &quot;test&quot; message<br/> - nothing interesting here except indentation.</div></td>
     </tr>
 </table>
                     </td>
@@ -987,7 +987,7 b' View Pull Request: http://pr.org/7'
     <tr><td height="10px" style="height:10px"></td></tr>
     <tr>
         <td>
-            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap;color:#395fa0"><div class="formatted-fixed">This PR is &apos;awesome&apos; because it does &lt;stuff&gt;<br/> - please approve indented!</div></div>
+            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap;color:#395fa0"><div class="formatted-fixed">This PR is &#39;awesome&#39; because it does &lt;stuff&gt;<br/> - please approve indented!</div></div>
         </td>
     </tr>
     <tr><td height="15px" style="height:15px"></td></tr>
@@ -1162,7 +1162,7 b' View Pull Request: http://pr.org/7'
     <tr><td height="10px" style="height:10px"></td></tr>
     <tr>
         <td>
-            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap;color:#395fa0"><div class="formatted-fixed">This PR is &apos;awesome&apos; because it does &lt;stuff&gt;<br/> - please approve indented!</div></div>
+            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap;color:#395fa0"><div class="formatted-fixed">This PR is &#39;awesome&#39; because it does &lt;stuff&gt;<br/> - please approve indented!</div></div>
         </td>
     </tr>
     <tr><td height="15px" style="height:15px"></td></tr>