Add waterfall display controls to the receiver windows

[bagmouse7]

The new wide bandwidth receivers allow you to create many virtual receivers that can cover many different bands.
This can create some display issues because the 80M bands noise floor can differ from the 20M noise floor, so the different receivers can be either too light or too dark.
Currently all of the receivers spectrum/waterfall displays are connected together and adjusted by the main spectrum/waterfall display control slider.

You can see in the screenshot below that the 2nd receivers display is "tuned" the way I like it, but the other receivers are all too dark.
It would nice to add individual waterfall controls to each of the virtual receivers.
Even nicer would be to allow each of them to be tuned individually, but allow them to still be tied together and controlled by the main displays slider controls.

Thanks!