Stop worker service automatically

[soygul]

The worker service which maintains connection to NBusy servers must stop after all of below are true:

• Work queue is done.
• Main application is killed -or- application is closed (i.e. no visible activities/fragments)
• A timeout of 3 minutes pass (in case user wants to go back to app quickly after closing it)
• http://stackoverflow.com/a/13809991/628273