Use LoD tiles, 3D and 2D, with lower zoom levels

[DerKarlos]

To reduce the GPU load, we need tiles with different LoD (Level of Detail) Actually use lod1 and also have lod2

• [x] lod2 is the more detailed one and should be used nearby
• [ ] lod1 should be used beyond a certain (dynamic) distance
• [ ] beyond a more far (dynamic) distance, 3D tiles should be used/replaced by 2D bitmaps (OSM,Sattelit)
• [ ] lod1/2 may need to be exchanged if the "player" moves
• [ ] lod1 and 2 are not much different in file size. We have to check about the GPU load and should ask Tobias toinvest, why.

The far tiles should be less but Zoom 15. The Sky needs to be set far away, even "infinite"

• [ ] Implementing with OSM bitmaps first
• [ ] until we get GLB tiles Zoom 14 etc.

See also #44

ADDENDUM: Tiles get removed quite fast now. Loading again is fast for the native build, not that fast for the Web. And at last, all the tile meshes need to be send in the GPU while the player may move and note small blockings.

• [x] Let's just hide them. And unhide it the camera turns back.
• [ ] Remove from GPU and memory only if much tiles are loaded, the oldest/most distanced first.

[oli-obk]