opengl demo visualization

[NicoKNL]

Based on some discussion between @RoanH and me, we figured it might be a good idea for now to have a 'default visualization' which demoes the functionality of the openGL draw methods. This way it stays modular and we can prevent merge conflicts on that.

[NicoKNL]

Working on this in the tree-map branch. When the tree-map visualization is considered done, I'll incorporate more information in the PR as well.

For now, it is used to highlight some basic usage of the openGL methods and provides some form of a measure-grid / origin widget. If there's something specific anybody would like to see, please reply here.

Current status:

[RoanH]

If there's something specific anybody would like to see, please reply here.

Is it too late for ellipsoids to be added to the demo 😅

[NicoKNL]

Nope, ill add them in

[NicoKNL]

Update

Now also includes ellipses, will be added through #66