Environment materials (does not work on all environments)

[Fernthedev]

Adds the ability to use materials loaded in the scene Example usage:

"_material": {
  "_shader": "BTSPillar" // takes precedences over "_shader"
}

Possible options as of writing this are:

• BillieWater - Uses the waterfall material (not the mirror distorted water)
• BTSPillar - Uses the BTS Pillar Cube material
• BaseWater
• BillieWater
• WaterfallMirror
• Obstacle (obstacle material)
• InterscopeConcrete
• InterscopeCar

This PR does not undermine the rest of the geometry functionality, as it allows for usage with different shapes and Unity scale. You can also color (animate) and change the shader keywords as expected.