[Base]: recents panel clear all button tweaks

- Show or hide recents button
- Place the button in top right or left

@cristianomatos

Conflicts:
	core/java/android/provider/Settings.java
Systemui: Recents - do not add search widget on recents if widget is lost.

We have reports that sometimes under special circumstances the widget gets lost
and the view is added nevertheless

Ensure that if the widget loading fails that the id is set back to -1 to remove
the view.

Change-Id: I62f8dcea19817a243a001c80b6a4ab7b1e31a990
SystemUI: Option to disable recents search bar (1/2)