FW_Base - Dispatch keys to a device specific key handler

Injects a device key handler into the input path to handle additional
keys (as found on some docks with a hardware keyboard).
Configurable via overlay settings config_deviceKeyHandlerLib and
config_deviceKeyHandlerClass.
DeviceKeyHandle: The device should consume only known keys
When the device receive the key, only should consume it if the device
know about the key. Otherwise, the key must be handle by the active app.
Also make mDeviceKeyHandler private (is not useful outside this class)
DeviceKeyHandler : Allow handling keyevents while screen off
Some devices require the keyevents to be processed while the screen
is off, this patchset addresses that by moving the filter up in the call
hierarchy.

Change-Id: I499392b743d975e8a2a602fc3e3d953a6ff6e009
Signed-off-by: Stefano Mura [STELIX PippoX3] <STELIX@gmail.com>