Release 2.0:
- add option to choose which detectors are active (#50)
- add option to delay unmute for a few seconds (#39)
- add option for always-on notification to prevent ad-free from being killed by
  OS. needed for devices such as MIUI. this includes a boot_completed
  receiver, alarmservice timer and runs the
  notification listener service in foreground (#51)
- overhaul of music plugin, use system own ACTION_OPEN_DOCUMENT_TREE
  dialog to choose music directory (#44)
- add option to loop local music plugin until end of ad (#48)  
- change how audio is muted. use setStreamVolume instead of
  adjustStreamVolume (#41)
- increase minSdkVersion to 23/ Android 6.0 (#19)
- UI optimized for tablets
