First draft of integrating radio support (#14)

This is a 1st version in order to integrate radio use cases into the current draft of the API. Main changes are:

1. A `ChannelAttributes` interface and sub interfaces to handle technology specific channel attributes were introduced. This should be needed for the different TV systems too.
2. Introduced a `TVApplication` interface. This interface could handle the different user applications, TV and Radio services might have. The design of this interface should not be considered final. Stream-related events would best be handled as data cues for instance.