Add instruction set dictionaries and ut_message conversion

* typesafe UT message type unique to instruction
** parameterized on: header alignment, common div / subword width
   (limited to integer type width), instruction dictionary,
   instruction
* instruction: { size, payload_type }
* supported instructions:
** JTAG (clock-scaler, init, instr.-register, data, data-response)
** timing (wait_until, reset)
** system (reset, halt, halt-response)
* {ARQ, Sim, Loopback}-connection
** common base in common namespace
** (parameter-)specialization for vx in vx namespace
** 'add', 'commit' messages to send to backend
** 'receive', 'try_receive' messages to receive from backend
** blocking 'run_until_halt' blocking until 'halt' instruction
   decoded (not available for loopback connection)
* remove unused python bindings in hxcomm
  due to missing-namespace-errors in generated code

Change-Id: I419a72e4f3c9a8e1bb6a92114d5f1f7cd5658df9