Restructure Sidebar for isochrone presentation

The presentation of the isochrone results in the sidebar is currently a bit overloaded with info.
Opacity is rarely needed for single isochrone rings and should be set once for one group.

Instead of having all isochrone rings in an array they should be grouped by the center they belong to so handling different isochrones is easier.
This needs some further refactoring as currently parts displaying admin boundaries for places as well as the print view for isochrones rely on the mapViewData.polygons being a single array of polygons to render.