Do not create MapTile objects unless necessary #6
Description
This could be redundant if issue #3 is resolved. However, it is worth checking.
Currently the map tiles are recreated every time anything happens. It would be more efficient to monitor changes in the set of map tiles that is needed and to only create new objects / trigger load operations for the tiles that were not visible before. However, this should done in a tidy way without leaking a whole hash map of all tiles ever created. Perhaps it could be resolved by extracting a stream of new tiles from the normal stream by retaining state in a map object and then using that as the source for the load flatmap. The place for this would be MapViewModel.