VCO attenuator On-Panrl Knob

[baconpaul]

Over in #569 during the beta period @rubyglow asked for a built in attenuator since the modules can run pretty hot in high unison with low detune and I added it to the RMB as a parameter

He has two suggestions for post-1.0 i want to record in a separate issue

• [ ] Add an overload indicator (perhaps a small red light at the outputs) which happens if samples go > 10v on a channel
• [ ] Consider an attenuator knob. I'm less certain on this one since it changes every VCO panel. But wanted to write it down

[baconpaul]

Overload stuff is dup with #617 so rename this and move it out of the 2.1 milestone