Proposal: add simple ADSR editor

[quirkylemon]

The current envelope generator is pretty intimidating for first time users so I propose that we add an option to use a simple ADSR envelope generator

this would just change how it is displayed.

1. the attack knob will just affect EG rate 1
2. the decay knob will just affect EG rate 3
3. the sustain knob will just affect EG level 3
4. the release knob will just affect EG rate 4

one issue is what to do when switching from the advanced EG to the simple EG.
2 potential options are:

1. pretend like nothing happened and just keep the knob positions even if the simple adsr editor can't change them.
2. give you a warning that you need to confirm then set the incompatible knobs to the default value (potentially saving them for if you revert back to the advanced EG)

I would be happy to implement everything.