[1/2] FB: Hardware Key Rebinding

Possible mapping
 0 - Nothing
 1 - Menu
 2 - App-switch
 3 - Search
 4 - Voice search
 5 - In-app search
 6 - home
 7 - back
 8 - toggle last app
 9 - kill app
10 - Go to sleep

Device overlay required

overlay/frameworks/base/core/res/res/values/config.xml
<!-- Hardware "softkeys" present on the device, stored as a bit field.
         This integer should equal the sum of the corresponding value for each
         of the following keys present:
            1 - Home
            2 - Back
            4 - Menu
            8 - Assistant (search)
           16 - App switch
        For example, a device with Home, Back and Menu keys would set this
        config to 7. -->
    <integer name="config_deviceHardwareKeys">7</integer>

This is a port/merge of:
https://gerrit.omnirom.org/#/c/2473/
https://gerrit.omnirom.org/#/c/4658/

Also requires Settings commit (https://gerrit.slimroms.net/#/c/2389/)
and overlay to function correctly

Change-Id: Ic5c9b4eb03d2baa3b0ddfb3e9fcaf10d6e45dcd3