Improvements to XTCE generator script(s)

[bourque]

We have scripts to generate XTCE-formatted XML files for each instrument (example here). These are used to generate the "packet definition files" which are used to decommutate packet data from the spacecraft.

There are some improvements we could make to these scripts:

• Make a single, generalized script that can process any instrument, instead of having a script for each instrument. This could be done by passing in command line argument(s) for the instrument to process, the path to the user's telemetry spreadsheet, the path to which to write the packet definition file, etc.
• Improve the information that gets printed to the terminal for the user. Currently it is pretty bare bones.
• Add appropriate unit tests