Add Tests

The current codebase is relatively hacky, with testing done entirely manually. We really need to automate as much testing as possible to make it easier to accept contributions.

For example, automating testing of radioreference site scraping & talkgroup extraction shouldn't be super hard. Make sure the script runs and outputs csv files. This will be very important for catching any breaking changes in radioreference's HTML tree that impact easily creating talkgroup csv files.

Other changes may be harder to test without trying them on a live system. This at least would require dedicated testing hardware, but changes may also depend on testing against certain P25 system characteristics, which may not be present where testing systems are available. This may just need to manual for now.

Start with the python utilities & helper scripts, and document manual testing steps for full, integrated systems.