Everything ties together in stream configurations, of which there can be many
now.

For the time being, every stream configuration but the "default" is ignored.

Every stream/server/encoder/decoder configuration now has the name "default"
by default, so that configuring names is only needed to resolve ambiguities.

Decoder configurations are now also constrained in this manner for consistency,
meaning they are no longer uniquely identified by a number of file extensions
but also a name.