Hardware key custom rebinding (1/3)

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
Overlay required
depending on the number of buttons on your device
<!-- Hardware 'face' keys 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>

Change-Id: I72c0d220a09d79230bfa299e0521ed693e5c25f1