Record feature

Add the possibility to record an avatar and then play back that recording.

Next PR will add:
- save/read recording from file.
- Script to manage all that.
The Avatar class gets the _recorder and _player, however they are only actually used by MyAvatar.  Does it make sens for any Avatar instance other than MyAvatar to use these?  If not then these members should be promoted to the MyAvatar class.  Otherwise they are fine here.