Add ability to change wavegen settings while it is running.

[samkristoff]

Changing the wavegen settings (like freq, wave type, etc) requires the wavegen to be turned off. Consider changing this to allow the user to make changes without explicitly turning the wavegen off.

This could be done in WaveForms Live by turning the wave gen off, changing the settings, and turning it back on, or it could be handled in firmware. The first option is easiest, the second would require fewer packets and therefore be faster.