Added complete scripting support for custom particles

[Semphriss]

Exposed API to allow scripting to:

• Spawn particles (Any amount, instantly or with respect to the "delay-between-each-spawn" attribute, etc.)
• Clear all particles on screen
• Get and set almost any property, and fade and ease any property for which fading and easing are relevant

[Semphriss]

NOTE: If you merge, please merge using squash. Only the message of the first commit is relevant. (Not relevant anymore)