ui: display editor only when it is ready

so it avoid strange ui effect when div get positioned

src/static/css/pad/layout.css

@@ -29,6 +29,9 @@ body {
   height: auto;
   flex: 1 auto;
 }
+#editorcontainerbox #editorcontainer:not(.initialized) {
+  visibility: hidden;
+}
 #editorcontainerbox #editorcontainer iframe {
   width: 100%;
   height: auto;

src/static/js/pad.js

@@ -573,6 +573,8 @@ var pad = {
       mobileMatch.addListener(checkChatAndUsersVisibility); // check if window resized
       setTimeout(function() { checkChatAndUsersVisibility(mobileMatch); }, 0); // check now after load
 
+      $('#editorcontainer').addClass('initialized');
+
       hooks.aCallAll("postAceInit", {ace: padeditor.ace, pad: pad});
     }
   },