[2/2] OmniGears: easy switch to soft keys

make it easier to switch to soft keys for devices
with hw keys. this is already possible now but the
settings are spread in different categories and require
multiple steps and using the property qemu.hw.mainkeys

this adds two new settings
1) allow enabling navigation bar during runtime on devices
that dont have it already enabled in the config.
This replaces the usage of the property qemu.hq.mainkeys

2) allow disabling hw keys (actions, brightness, haptic feedback)
with a single setting. This requires that the device supports
config_button_brightness_support config_has_hardware_buttons
and config_deviceHardwareKeys

as part of this the button brightness settings screen
has been moved to a separate screen

TODO: disable google search on long press menu

Change-Id: I06eedf26abd2885b711321193e9a486c08a5e192
Merge pull request #13 from omnirom/android-4.4

[2/2] OmniGears: easy switch to soft keys