Keep main activity when recording is cancelled

When a recording (running in background) is stopped and the user
returns to the FM app, the recording activity is seen with a 'Save
Recording?' popup. After responding keep/discard the app exits itself
instead of returning to the main activity.

This happens because the service calls exitFm() and activity finish()
when the service receives the musicservice 'pause' command (e.g. when
the camera starts).

Instead of a complete shutdown, stop recording and pause (powerDown)
the FM playback. This leaves the service in a funtional state and the
recording activity can save/discard the recording and return to the
main screen.

FEIJ-1373

Change-Id: Ia3209b32cea193e76fb7b0b26b1ba05b88bd9d2c
(cherry picked from commit 480142b3)