Enable custom actions for double-tap home (1/2)

PatchSet1: add custom actions
PatchSet2: set defaults
PatchSet3: try to get defaults from config.xml
PatchSet4:
* do get defaults from config.xml
* store state of HARDWARE_KEY_REBINDING
* removed trailing whitespaces
PatchSet5: merge with 48002
PatchSet6: getting late, forgot to change the title when merging
PatchSet7: remove whitespace trimming, reduce code duplication
PatchSet8: rebase, simplify code

Change-Id: I041e7ab3853b356ddbdab2524f096546319276f9