Added simple particle system with couple of implementing classes and ready-made effects.
- Particle: Structure for single particle
- ParticleSystem: Contains single particle system
- ParticleBehaviour interface: Manages how single particle behaves
- ParticleEmitter interface: Manages what kind particles are emitted from particle system.
- ParticleSequencer interface: Manages when particles are emitted
- ParticleEffect: Combines the above into a single effect
- ParticleManager: Manages ParticleSystems and ParticleEffects