Lockscreen Targets : Fix empty magnetic behaviour

When no valid targets are set, set settings to null in order
to enable magnetic targets (aosp behavior)

Change-Id: I0ccaad25cc85f55b99e4c34cb4ffe2d06bda4a80
Fix adding apps to lockscreen targets without explicit icon selection.

Change-Id: I28c5a2fb72aabd892cc861d592ef20bcbf9fb891
Clean up lockscreen target configuration code (2/2)

Get rid of a lot of duplicated code.

Change-Id: I03faf36d5e767053072f1809f670882600ea0830

Conflicts:
	src/com/android/settings/cyanogenmod/LockscreenTargets.java
Avoid NPE if icon assignment failed for whatever reason

Change-Id: I879b8c6f52631fe9f02150cfae5c9a7cfa35ea61
Fix adding lockscreen targets.

The empty targets were not included in the setting properly.
Also make the code a little more memory efficient.

Change-Id: I05cc7ce55ef5789f063033116ebfd9337e5ee28a
Lockscreen targets: more unification

Use shared method to derive drawable inset and make the rounded
corners for icon files also display when adding the target initially.

Change-Id: I98ea3e522c4c6240f08e11007d53509a3d2c15f8