framework: move device key handler logic, fix gesture camera launch

In order to make device camera gestures behave the same way as launching
the camera by double tapping the power button, route DeviceKeyHandler
logic through the GestureLauncherService.

A callback is used in order to avoid publishing the
GestureLauncherService into the System service registry, because the
KeyHandler code cannot directly access services local to the system
process.

OPO-427

Change-Id: I2a8860b278f65ccf31bfee151513d8a23ab746c5
Signed-off-by: Roman Birg <roman@cyngn.com>
(cherry picked from commit db1b4e6e)