Updates for 1.2/26

He is a bunch of updates for 1.2 version.
First a quick update to the latest aurora builds, that allows to drop some workrounds. (I requested uplifts for the others)
I added yet another workaround (I still need to craft a patch against b2g desktop, for the contenBrowser/shell.start being accessed or called too early) in order to prevent a race condition where we would end up with the reg logo or a black screen on startup.
Also an update of the label being displayed in the app manager, so that we end up displaying "Firefox OS 1.2". (I think that what we agreed on irc?)
Finally, some cleanups in prosthesis to remove non-working UI elements and duplicated actors.