Implement logic data muxer thread

Implement logic data muxer thread

Multiple changes in one commit due to complexity:
1) data::decode::Decoder: Make use of the DecodeChannel struct for
channel assigments

2) DecodeSignal: Store DecodeChannel list in vector, not map

3) DecodeSignal: Remove unused get_data()

4) Remove boost::optional usage

5) Use DecodeSignal::segment_ as the container for muxed
logic data

6) Implement the DecodeSignal::logic_mux_proc thread and its
helper method mux_logic_samples()

7) Update DecodeSignal::decode_proc() to interface with the
logic muxer thread

8) Remove no longer needed DecodeSignal::wait_for_data()