Cleanup after #88

[epost]

• This clzz thing is defined in multiple places; centralise it? A better name would be nice too.

  clzz :: Array String -> H.IProp _ _
  clzz strs = classes (ClassName <$> strs)

• The Vec stuff in in Data.Vec2D.
• The Box stuff in Data.Vec2D, introduced because of PNPRO text-boxes
  • Reconsider wh, used to compute width and height, see here.
• Reinstate buttons to enable/disable labels on places, transitions, arcs.
• Place properties editor should be styled using Tailwind CSS