Add a way to export plan as an image

[joelspadin]

Currently, the easiest way to share an image of a plan is to take a screenshot of it. That's cumbersome to do for plans with multiple steps.

I should add some way to get the current step as an image (ideally by putting it directly on the clipboard, but downloading would work too), and possibly add a way to get the whole plan as an image with steps in a grid.

[joelspadin]

I've added a way to copy the current step to the clipboard as an image. Adding a way to export the whole plan as an image (in a grid with a configurable number of columns?) would be a good improvement on this.