ModAPI SDK v2.5.567

Make `cPlanetModel` actually usable (#113)

* Improve terrain-related class fields, add `cTerrainSphereDecal`

* Add `cTerrainSphereDecal` to `Terrain.h`

* Minor field renames

* Fix includes in `cTerrainSphereDecal.h`

* Minor field fix for `cTerrainDecal` (68h is some float value)

Also rename some fields in `cPlanetModel`.

* Rename fields of `TerrainModification` (a.k.a. `cRelevel`)

* Describe most `cPlanetModel` fieldss, fix alignment