Suggestion: FFPlay volume save

[Watermelonfiend]

On the MMP, when opening a new video, the volume starts very loud, even if the previous video that was opened was soft or off. Recommend volume saved over when exiting videos or if there's a system wide volume it can mirror when launching videos.

[goweiwen]

This affects all apps that do not use audioserver. We need to implement a way for apps to specify that audioserver is not needed, so alliumd can automatically:

1. kill audioserver
2. start the app
3. set volume back to previous level
4. when the app closes, restart audioserver