Implemented Improved Perlin Noise in existing "textured voxels" option.
TextureCache.cpp: modified so that permutation texture contains known permutation of 0..255 rather than random set of values. Does not noticeably affect visuals.
perlin_modulate.frag: implementation of improved noise, per 2002 SIGGRAPH paper, including "turbulence" summation.
Merge branch 'master' of https://github.com/highfidelity/hifi
Fixing up #define / #if pair so that permutation table change can be turned of by setting #defined variable to 0 instead of having to comment it out.
Merge pull request #3111 from noirsoft/master

Implementing improved perlin noise