add settings, allow to configure "show touches"

everyone likes to configure stuffs, so allow them to.
first option is the initial state of "show touches" when starting
a screencast, which is enabled by default

Change-Id: I65b7f9249624085107269e7ea49876ee72f346d1
update notification immediatly when toggling touches

else it still shows the previous state until the
notification update timer kicks in, which runs every second

also remove the useless context argument

Change-Id: I4ce51473ea826bdc67524bec0c86ab09c36edcee
allow to delete screencast via notification

Change-Id: I5e5ccb9a65040c4fe17df11cfb2c0df154ae35e5