Lock the buffers when modifying them.
Notify when callers change a set avatar image.
Create a get function for images.
Allow deletion of previously loaded images, and reuse of their ids.
... changes.
Implements STEAM_CALL_RESULT( AvatarImageLoaded_t ).
Adds support for a sending a STEAM_CALL_RESULT( PersonaStateChange_t ) with the k_EPersonaChangeAvatar flag.
Creates a mapping in Settings to hold the avatar image data.
Also adds additional debug logging to indicate which image handle is
returned for each user / image size.
