Set volume to 50% for new paired headset

Set volume to 50% for new paired headset instead of using current media
volume. Remove stored volume when headset is unpaired.

Bug: 126280577
Test: Manully pair/Unpair headset, switch active device.

Change-Id: Ibfcde0c04318a17664db1649dd1f3c21dc8f99c8
3 files changed