Renamed ParticleEmitter to ParticleSystem
Added class ParticleEmitter
(First implementation, this will probably change)
Former-commit-id: a1f80db340983da5e85cedc974dd6b24a98e25b0
Switched back to defaulted operator=(ParticleEmitter&&) since it can't
throw exception anyway
Former-commit-id: 178b040a735ef01dcda21b45a317b6c534b5782e