Queue improvements and misc fixes

* Setting max-size-time which is a guint64 with a regular integer constant was bad. :grimacing:
* Having one thread from the jitterbuffer all the way through decoding, scaling, colour space conversion, to the sink was bad. :grimacing:
* Comparing a double to an integer was bad. :grimacing: 
Still having 2 or 3 here would be better :)