Expand Map Viewer functionalities

[jahow]

The following features will be added to the Map Viewer app:

• [x] Add layers from third party sources: WMS, WFS, OGC API Features, GeoJSON file
• [ ] Manipulate layers: order, opacity, delete
• [ ] Zoom on a layer extent
• [ ] Show the map legend
• [ ] Import and export a map using a JSON-based file format
• [ ] Print the map in PNG or PDF
• [x] Add a geocoding widget
• [ ] Show current user location
• [ ] Show cursor coordinates (both in map projection and geographic coordinates)
• [ ] When using the map viewer web component:
  • [ ] Ability to specify a map JSON and make it read-only