Load vector tiles into basemap

[karelleketers]

[pietervdvn]

• Start from the master branch, create a new branch from there (feature/vector-tiles)
• Have a look at what vector tiles are
• Have a look leaflet.js docs (also see minimap.ts)
• Have a look at the leaflet vector tile plugin

[pietervdvn]

Also relevant: BaseLayers.ts

[pietervdvn]

Superseded by #1182