Engine trails

Current state of the Engine Trails
* Adds Engines to Ships
* Engines have a EngineTrailGenerator
* Rockets are Ships (to be changed once an EngineController or similar is introduced)
* Make Normandy, Wall & Planet lockable
* Fix color of enginevoxel in basicship
* Contains vao and emission PRs (review those first)
* Removes some Voxel* prefixes
* Introduces/refactors ParticleSpawnBase, DebrisGenerator and ExplosionGenerator