add test_mux() to OhmPi and a bit of file tidying.

Closes #77

See merge request reversaal/OhmPi!13

Adds basic_ohmpi_flows_node-red. Updates architecture.pdf. Moves mqtt_controller.py in examples and updates it.

Merges changes on both sides on _process_command. Adds cmd_id to exposed functions for in function messaging

current parameters, not just for debug I think)

Fixes issue #77. Improves args and kwargs handling by _process_command. Reorders method in alphabetical order to ease navigating the code