[launcher] Drag’n’dropped favorites not persistent

[Olivier Tilloy]

Steps to reproduce:

1) Run `nautilus /usr/share/applications &`
2) Drag any icon (e.g. "About Ubuntu") from the nautilus window to the launcher and drop it there
3) Observe that the application is added to the launcher and can be launched
4) Logout, or simply restart the launcher: `killall unity-2d-launcher`

Expected result: the icon of the application previously favorited via drag’n’drop is still there
Current result: the launcher "forgot" about this favorite application

[Olivier Tilloy (osomon)]

Note that the cause of this issue is quite obvious from reading the code: drag’n’dropping a desktop file to the launcher invokes LauncherApplicationsList::insertFavoriteApplication(…), which never actually calls LauncherApplicationsList::addApplicationToFavorites(…).