base: tweaks to support force usage of soft keys for devices with capacitive buttons

Two minor tweaks to support that use case.
For devices with capactivive buttons disabling those buttons
need two steps

1) disable buttons backlight - dark mode
2) settings - buttons - custom actions and set all buttons
to "no-action". This fix is needed to get a working home button
and working "long press back to kill" for that setup

PS5
better solution

PS6
cleanup

PS9
whitespace

Change-Id: I563e877580c09df45383e4485c6cbb965aca0b31
Merge remote-tracking branch 'cm/android-4.4' into android-4.4