Fixing CM3 style related issues.

CM3 introduced a number of changes to how various paddings are set.
Because of how we change the line-height we had to set these back
to the CM2 values. What a pain!

IPython/frontend/html/notebook/static/css/style.min.css

@@ -916,6 +916,8 div.text_cell_input{color:#000000;border:1px solid #cfcfcf;border-radius:4px;bac
 div.text_cell_render{outline:none;resize:none;width:inherit;border-style:none;padding:5px;color:#000000;}
 .CodeMirror{line-height:1.231;height:auto;background:none;}
 .CodeMirror-scroll{overflow-y:hidden;overflow-x:auto;}
+.CodeMirror-lines{padding:0.4em;}
+.CodeMirror pre{padding:0;}
 .ansiblack{color:#000000;}
 .ansired{color:darkred;}
 .ansigreen{color:darkgreen;}

IPython/frontend/html/notebook/static/less/notebook.less

@@ -378,6 +378,18 div.text_cell_render {
     overflow-x: auto; /* Changed from auto to remove scrollbar */
 }
 
+.CodeMirror-lines {
+	/* In CM2, this used to be 0.4em, but in CM3 it went to 4px. We need the em value because */
+	/* we have set a different line-height and want this to scale with that. */
+	padding: 0.4em;
+}
+
+.CodeMirror pre {
+	/* In CM3 this went to 4px from 0 in CM2. We need the 0 value because of how we size */
+	/* .CodeMirror-lines */
+	padding: 0;
+}
+
 /* CSS font colors for translated ANSI colors. */