Plot Workbench aligned to guidelines

[agryson]

Here are the plot workbench icons aligned to guidelines.

16,24,32,64px on light, gray and dark backgrounds with old on left, new on right.

spritesheet.png (261.09 KiB) Viewed 1000 times

Given that Ship workbench hasn't been submitted yet, I'm probably going to submit both of them in the same pull request.

Things we'll need to change here include removing the graph background from most icons, it's unnecessary and reduces form contrast.

Feedback welcome.