Docs and changed to unique_ptr ParticleGenerator

[DunderRoffe]

Started to write documentation for ParticleGenerator and half way through I noticed that there were some parts that could easily be cleaned up, so I did.

• The constructor no longer takes a model matrix. Instead the attached GameObjects model matrix is used instead.
• There are no longer any traditional pointers used. Instead ParticleGenerator uses std::unique_ptr. This is especially nice since the Particles are automatically cleaned up which did not happen at all before.

[DunderRoffe]

Moving this to my fork