Revert "Settings: disable lock screen heads up (2/2)"

This reverts commit 62559b70a69f0ba052202952b32a426a2ae0279a.
Heads up: enable heads up notification checkbox for all

- Disbale check of system packages to allow checkbox for all. This will, for example, bring screenshot to heads up if SystemUI is enabled

Change-Id: I273caffa992e79a9a9d6914bf1c89f9388044da4
Heads up: option to disable in lockscreen (2/2)

Change-Id: Icbc6fba1727c009f7ea42a66ea3167f19d527e10

Conflicts:
	res/values/cr_strings.xml
	src/com/android/settings/liquid/HeadsUp.java