Revert "Revert "Reduce observers in SystemUI: StatusBarIconView""

This reverts commit bb4be8ea49df2529d253468c4dcbc84bdf8128aa.
Revert "Revert "Fix SystemUI memory leaks on theme changes.""

This reverts commit 61086b357aa052a1204abd972ff29c27eaf9409c.

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/policy/Clock.java