Add minimap + toggleable button to show on the lower right

[gk646]

Similar to paint.net a minimap would b a cool feature The button goes next to the other toggleable on the top right.

The minimap should only show visible nodes. It should show rectangles of the node outlines. It should be zoomed out slightly further than the current screen to give an overview. Optimally the minimap should be scaleable and dynamically resizable by the user.