rename "new-file" to "new > text file"

Because it is not obvious to everyone...

Closes  #7571

IPython/html/templates/tree.html

@@ -44,7 +44,7 b' data-terminals-available="{{terminals_available}}"'
                   </button>
                   <ul id="new-menu" class="dropdown-menu">
                     <li role="presentation" id="new-file">
-                      <a role="menuitem" tabindex="-1" href="#">File</a>
+                      <a role="menuitem" tabindex="-1" href="#">Text File</a>
                     </li>
                     <li role="presentation" id="new-folder">
                       <a role="menuitem" tabindex="-1" href="#">Folder</a>