Update meta file sections for clarity of purpose

[asgibson]

The meta file, which contains information about what received telemetry is expected to look like and how that relates to the running of OnAIR should be examined/updated to make usage more clear.

Specifically, we should discuss whether the "subsystems" label still makes sense and if "order" is descriptive enough to explain what it is.

[asgibson]

For the "order" section, using "frame_order" or "low_level_data_headers" may be more appropriate and descriptive of its use within OnAIR.