Add a scale parameter to FCS generation

[atruskie]

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

Sometimes the FCS images are just too small. This can be the case when using them in slides, or print outs, or publications that require a high DPI.

Describe the solution you'd like

Even though there isn't any extra data available, we'd like to see the images made bigger. Simply by repeating pixels like a zoom factor.

Possibly: add an ImageScale integer config parameter to the SpectrogramFalseColourConfig class.

Even though the FCS spectrogram data should be scaled, the image chrome (title, axes, legends) should not be scaled.

Describe alternatives you've considered

We could interpolate, or window, or do some other fancy data stitching. That takes effort though.

Additional context

This issue was filed on behalf of an external collaborator.