Models with high priority will be favored over models with low priority.
Recordings for models with low priority might even get stopped to free
up a slot for a model with a higher priority
Since MFC uses different streaming technologies, the stream sources have
to be determined differently. This is now done in dedicated
StreamSourceProvider classes.
Add createDownload to Model. This method is called by the recorder to create
and then start a download. It is a method of Model so that each site and
each download can create a specialized download.