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.

Change-Id: I6678c89c7530fdb1d4d516ba4f1d2c9e30ce79a4

Conflicts:
	core/res/res/values/symbols.xml
Merge "Dispatch keys to a device specific key handler" into cm-10.1
Merge remote-tracking branch 'upstream/cm-10.1' into cm-10.1