Adjust widths of bubbles and chat window

With these changes, message bubbles in the default-sized chat popup are
just wide enough to display the full complement of html5 media player
controls.

js/panel_controller.js

@@ -57,7 +57,7 @@
                 url: 'conversation.html',
                 type: 'panel',
                 focused: true,
-                width: 280,
+                width: 300,
                 height: 420
             }, function (windowInfo) {
                 windowMap.add({ windowId: windowInfo.id, modelId: modelId });