Do not launch floating window when on default launcher

We only do this when user is on the default launcher
because if the user was on a non-default launcher,
he/she must have been there for some purpose and we
do not want to throw him/her back to the default
launcher incase he/she exits the app with HOME button.

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/notification/NotificationHelper.java