Bug 898647 - Backend for app updates. r=myk,fabrice

--HG--
rename : browser/modules/webappsUI.jsm => browser/modules/WebappManager.jsm
rename : toolkit/webapps/WebappsInstaller.jsm => toolkit/webapps/NativeApp.jsm
rename : webapprt/WebappsHandler.jsm => webapprt/WebappManager.jsm
extra : rebase_source : d009be9de28cb917062d567592f773e9ece4266e