Bug 852516 - Fix timing issues in contacts app (initial load). r=albertopq

Fix for [#852516](https://bugzilla.mozilla.org/show_bug.cgi?id=852516). Before the contacts list gets loaded the `ContactsList` first needs to be initialized. Thereafter we need to have loaded the async scripts before starting to render the actual contacts because we rely on certain util scripts to be there (escapeHTML f.e.). This PR addresses that.

On the expected reply: "but it works on my device". Sure it does, but there are timing issues, and they will probably show up at one edge case or another, I have already run into them so probably someone else will too.