Triplanar terrain + Better terrain normals

[JamesTKhan]

• Adds Triplanar option under terrain settings
• Overhaul Terrain Normals. Improves terrain normal calculations and accuracy at the cost of additional memory by averaging the normals
• New CLI argument to disable shader preprocessor caching for development purposes

Triplanar should work on terrains up to 252 Vertex resolution

Note: Triplanar is not always better, it is situation depending on your terrain. Triplanar is more expensive (more texture sampling) and can look bad with lots of sharp edges close together, etc..

Once Merged I will start putting together the 0.5.0 release

Dependent on merging #176

Triplanar On/Off Comparison

Before Terrain Normal overhaul:

After Terrain Normal overhaul:

[JamesTKhan]

Made obsolete by #184