Offline tile cache

[steff-o]

Is your feature request related to a problem? Please describe. When no network is available it is not possible to navigate in the map as tiles can't be downloaded.

Describe the solution you'd like Before the user enters an area with poor network coverage it should be able to prefetch tiles from WMS/WMTS to a local persistent storage that Origo can use as source.

Describe alternatives you've considered Going native.

Additional context We have made a PoC that creates an offline OpenStreetMap source class that replaces the built in source. The offline source is capable of prefetching tiles to a persistent storage och redirect the requests for tiles to that storage. The same approach would be possible for tiled WMS and WMTS.