Recents clear all app lock option.

Apps can be locked and unlocked from being clearable in
the recents panel by selecting the option in the popup
menu when long pressing the item.

PS2:
Remove commented out line and add method descriptions.

PS3:
Persist locked tasks.

PS4:
Use persistentTaskId.

PS5:
Fix landscape layout

Change-Id: I254ecbe45c14d47a60e7d39c011421e4c9c276a0

Conflicts:

	packages/SystemUI/res/menu/recent_popup_menu.xml
	packages/SystemUI/res/values/vendor_strings.xml
	packages/SystemUI/src/com/android/systemui/recent/RecentsActivity.java
	packages/SystemUI/src/com/android/systemui/recent/RecentsPanelView.java