[UI Request] Volume envelope value display

[Pegmode]

I'd suggest adding a readout of the actual envelope values in the instrument editor.

The reasoning is that with the current implementation it's very difficult to reference volume levels relative to each other. For example if I want to use a Cxy command, in order to know exactly what volume level I should be starting at I have to count the ticks on the slider bar; which is tedious and time consuming.

It also makes making instruments relative to each other a bit more difficult.