helpers: add material like checkbox

Orginally developed by @navasmdc
https://github.com/navasmdc/MaterialDesignLibrary

Apart from huge memory optimizations for the onDraw() and
some other smaller things, i also added the ACTION_CANCEL
event so the view would behave as expacted.

Signed-off-by: Blechd0se <alex.christ@hotmail.de>
android: implement new checkbox style

Just the follow-up commit to the last one, which replaces
all checkboxes on our custom preferences with the new ones.

Signed-off-by: Blechd0se <alex.christ@hotmail.de>
service: check for null on stopService()

If the helper class and the service was out of sync because
of whatever reason we could end up in a null pointer while
we try to stop the service.

Signed-off-by: Blechd0se <alex.christ@hotmail.de>