Add BAMF theme engine

Thanks to travp624 @ TeamBaked for originally porting this

Change-Id: I9dd9347ac62e3b1fb49a4562d84eb7b295cdc2b2
Revert "Reduce observers in SystemUI: KeyButtonView"

This reverts commit 176e83558d0a8bb537c44bcc4c7325cb2451f9ad.