[dab] DL+ carousel

[hairmare]

As a user i would like have my receiver know about metadata.

The spec defines quite a few metadata fields that we would like to support in addition to ITEM.TITLE and ARTIST.TITLE as done by #130.

• STATIONNAME.SHORT = "RaBe"
• STATIONNAME.LONG = "Radio Bern"
• PROGRAMME.NOW = current show
• PHONE.STUDIO = "031 330 99 99" (only during live shows?)
• ...

The way to do this is to rotate through a bunch of strings with different content. ODR-PadEnc supports this out of the box, I'm not sure if ODR-EncoderManager supports this yet.

For some of the fields we already have data available, other might need ingesting of data from somewhere.

A complete list of the fields is defined in nowplaypadgen, we'll want to check them to see which are applicable to our case.

[hairmare]

might be implemented with collections.deque as a round-robin ringbuffer of sorts

[hairmare]

need to clarify if this is supported directly by SMC