Portals levels in layer chooser

[johnd0e]

We rarely need to fine-select exact portals levels to show. And those portals checkboxes take too much space in layer chooser.

What we can do:

• use custom hierarchical layer chooser, like here:
  • https://github.com/McBen/ingress-intel-total-conversion
  • https://github.com/bambrikii/leaflet-layer-tree-plugin
  • https://jjimenezshaw.github.io/Leaflet.Control.Layers.Tree/examples/
• use completely different control, like ingress stock.
• use simple dialog (or even plain text inputbox)