VFX16 Prototype Testing

This is a prototype for a particle system generator. The goal is to test the idea and get some feedback.

Some known issues:

• Godot export is disabled pending this Godot PR.
• The generators need more variety.
• Safari on macOS has various problems like window size and performance.
• Trails don't seem to be working in the web tool but they should appear in your export.
• Second and third textures on 3D meshes can have artifacts at the mesh boundaries (like the 3D fireball) but this is a web rendering error. Exports should look fine. 
• Manually entering scale values for an emitter doesn't work reliably. Better to just use the widget.
• There's no way to reset the camera view, so you can get lost sometimes.
• There's no toggle for world vs. local space yet. Would be very handy.
• It'd be nice if there was a way to loop playback of one-shot effects like explosions.
• Can't tab between text boxes.