HTML validation: Add placeholder text to <h1>, <h3>.

Otherwise validator.nu warns about the empty header tags.  The
placeholder text is replaced by JavaScript.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

templates/zerver/app/settings_sidebar.html

@@ -1,6 +1,6 @@
 <div class="form-sidebar">
     <div class="title">
-        <h1></h1>
+        <h1>Title</h1>
         <div class="exit">&times;</div>
     </div>
 

templates/zerver/integrations/index.html

@@ -117,7 +117,7 @@
                 <div id="integration-instructions-group">
                     <div id="integration-instruction-block" class="integration-instruction-block">
                         <a href="/integrations" id="integration-list-link" class="no-underline"><i class="fa fa-arrow-circle-left" aria-hidden="true"></i><span>Back to list</span></a>
-                        <h3 class="name"></h3>
+                        <h3 class="name">Name</h3>
                         <div class="categories"></div>
                     </div>