Bug 1112135 - [Messages] When starting as an activity/notification/, delay threads rendering until the right panel is open. r=julien

> I had the impression that it was not; if it is then I'm fine.

I've moved ```ThreadListUI.init();``` here from ```loaded``` to reduce delay before lazy loading is started as you noticed. So only ```MessageManager.init();``` and ```Navigation.init();``` left, the latter is better to have before lazy loading since we call ```Navigation.getPanelName()``` that potentially can depend on ```init```, the former doesn't look like a "heavy" call. 

Does it work for you @julienw ?