Mainly support for OpenRTX.

The proper support for OpenRTX requires some preparation. As there are new contact and channel types, I first need to implement some sort of intermediate codeplug representation (IR) before encoding them into binary formats. This IR will strip all features not supported by the target radio, split/merge zones if needed etc. The limitations of the radio will then be checked against the IR. This also eases the encoding/decoding of the binary codeplugs. So having an IR is a good idea anyway.