stop playback before changing track
add TODO for VariableContainer_new() arguments
add TODO for resolving modules cross-dependecies
clean up comments
copy-paste is a BAD THING
pretect access to variable containers

service-level mutex was only used to protect access to variable
containers, and notifications thread did not protect access to
containers

The mutex was moved to variable container, and is now used in all places
where variable containers are accessed.

Also, the notification code was improved to make sure variable changes
are not missed
primitive events moderation