WIP: Improve inter plugin by introducing new overflow-mode property and fixing interaudio behavior
This applies two major changes:
- All inter*sink elements get a new
overflow-mode
property to determine what happens when the inter channel is full (either block the sink until the channel has some spare capacity, or overwrite the oldest data in the channel). - Fixes to behavior in interaudiosink/src are applied (draining samples during a caps change & inserting nullsamples correctly).