Add the ability to send raw MDC commands

[peternewman]

To handle new things or features we don't currently support.

[ltuaehome]

What's the correct format for custom commands? Attempting to use hex codes, that I know work with the generic tcp module from companion 3.3, but they don't work through this module. (and thanks for all the work done on this, testing the latest release 2.0.1)