Improve 2D plots

[andeplane]

The 2D plots are close to finished, but needs some fixes.

• [ ] Use quick controls 2 to have the same dark theme as the rest
• [ ] Fix Qt datavis styling
• [ ] Should we allow rotation of the plot (it is 3d)?
• [ ] Remove window when simulation has stopped
• [x] Fix so clicking on a compute twice doesn't open two windows.

[andeplane]

Currently these don't work, but we'll fix this here.

[andeplane]

They now work, but we still need to do the fixing above. We move to 2.1.