v10: Backport of Elevation Data Storage

Backport from v0.5.1 of storing the elevation data for each scene as a webp image in worlds/[world-id]/assets/elevatedvision/[world-id][scene-id]-elevationMap.webp. Previously, the elevation data was stored in the scene flag. Switching to storing an image should be faster by avoiding database churn. Avoids a potential v10 database issue that could cause the world not to load if the length of the elevation data got too long.