Make screen_service() useful for more than services

screen_service() can currently only be used to launch things that
pass the 'is_service_enabled' check, even though its calling functions
will have already done this.  This removes such check, renames it
to screen_process() and updates its usage elsewhere.

Change-Id: I480a4560a45b131a95c1b2d2d2379aeba542a9bc
Merge "Make screen_service() useful for more than services"