Add headings for dialogs

Keep them in the same style as the panels.

vnc.html

@@ -277,6 +277,9 @@
     <!-- Server Key Verification Dialog -->
     <div class="noVNC_center noVNC_connect_layer">
     <div id="noVNC_verify_server_dlg" class="noVNC_panel"><form>
+        <div class="noVNC_heading">
+            Server identity
+        </div>
         <div id="noVNC_fingerprint_block">
             <label>Fingerprint:</label>
             <div id="noVNC_fingerprint"></div>
@@ -294,6 +297,9 @@
     <!-- Password Dialog -->
     <div class="noVNC_center noVNC_connect_layer">
     <div id="noVNC_credentials_dlg" class="noVNC_panel"><form>
+        <div class="noVNC_heading">
+            Credentials
+        </div>
         <div id="noVNC_username_block">
             <label>Username:</label>
             <input id="noVNC_username_input">