Create an option to switch band power widget to linear scale

[philippitts]

Is your feature request related to a problem? Please describe.

The band power widget currently shows powers on a logarithmic scale. This is useful in many cases, but in some cases it does not provide enough detail when trying to observe small differences in band power.

Describe the solution you'd like

Create an option to toggle the scale of the band power widget graph between linear and logarithmic.

[retiutut]

I think it could be better to show Average Band Power data as displayed in the Focus widget. Could pocket the "old band power data" which is based off of the minim FFT library as an alternate mode accessible via a dropdown.