TileJSON discovery (similar to WMS and WMTS)

[ThomasHalwax]

1. Enter a mbtileserver URL (e.g., http://localhost:8000/services)
2. ODIN detects the JSON array and shows available tilesets with checkboxes
3. Select the tilesets you want (just like WMS/WMTS)
4. They appear in the background maps control where you can adjust visibility, opacity, and rendering order