FW: Add "Clear All drawables" for NavBar

This is a part of "Recents: Clear all button for recent apps." from PA

Only for show in Lockscreen when are notifications

PS2: Update author & message
PS3: Damn damn I put the drawables in the wrong place...
PS4: Added missing import

Change-Id: I9164ef632d7d7bc31d81bb7a6d87c5d1562d5410