Image Screenshot Exports

[ilan-gold]

User story
From Laura:

And would be nice to be able to export png/jpg image for example for presentations just with the chosen channels not the whole dataset. Ideally, then on the image the chosen antibody targets and colors would be automatically displayed (with an option not to include that) together with the scale bar. 

Preferred solution
Add a new button in the "Settings menu" for the screenshot of the current canvas

Possible alternatives
Maybe it could be per layer somehow and in the layer controller, or in a settings dropdown there? Maybe just a hover over the canvas, like the pointer arrow?