Bug 1073520 - Optimize render time of panels in settings app

There are potential issues of doing transition before the scripts get loaded.
1. Users may interact with the UI before the scripts are ready.
2. There is no chance for a panel preparing its content before presenting to users.

The first issue could be solved easily by blocking all touch events before everything is ready. As for the second one, it seems a UX tradeoff between responsiveness and attractiveness. We may need some UX inputs in order to strike a balance.