Clean up lockscreen target configuration code (2/2)

Get rid of a lot of duplicated code.

Change-Id: I03faf36d5e767053072f1809f670882600ea0830

Conflicts:
	res/layout/lockscreen_shortcut_dialog.xml
	src/com/carbon/settings/fragments/IconPicker.java
	src/com/carbon/settings/fragments/LockscreenTargets.java
Avoid NPE if icon assignment failed for whatever reason.

Change-Id: Iba4188d6b42179008154b8cbcbb14c36a22669de