Prismarine Shader

Features added/changed:
+ Added aurora contribution to sky lighting. No performance impact
+ Added several super secret options. Go find them :)
+ Added new filters for volumetrics
+ Added half resolution rendering to SSPT and volumetrics. Resolution can be changed in settings
+ Changed GLSL version to a newer one
+ Added new emissives to integrated emission
+ Added new nebulas which cost almost no performance
+ Added constellations
+ Optimised and heavily modified exponential and distant fog
+ Optimised and heavily modified volumetric clouds and light shafts
+ Optimised and improved bloom
+ Optimised and modified DoF and distant blur
+ Modified nether portal texture
+ Modified underwater lighting and fog
+ Modified water absorption and translucency blending
+ Added rainbows
+ As always, did a lot of config tweaks and changes

Features fixed:
Fixed some light sources not being emissive with SSPT
Fixed chests and entities being half-transparent with SSPT
Fixed night vision fog
Fixed several program errors which were occurring after enabling some options
Fixed both volumetric and exponential fog breaking in deep caves

Features removed:
- Procedurally generated nebulas