Bug 1103922 - [Loop] move lazy loaded [BB] to index.html

Should we load `list.css` and `edit_mode.css` as well? We have them in https://github.com/mozilla-b2g/firefoxos-loop-client/pull/326/files#diff-3db19adbd2e8ba7dbf2474648a24169dL272, but I dont know if it's dead code or not. Could you review it?