Support for clip/cull planes in ES: EXT_clip_cull_distance

EXT_clip_cull_distance exposts ARB_cull_distance to GL ES.
https://www.khronos.org/registry/gles/extensions/EXT/EXT_clip_cull_distance.txt

It looks like the version/profile requirements in Initialize.cpp will need updating to include ES for the following:
gl_ClipDistance
gl_CullDistance
gl_MaxClipDistances
gl_MaxCullDistances
gl_MaxCombinedClipAndCullDistances

Also just to double check, the version number requirements for cull distance are 450, but only OpenGL 3.0 is required. Is this because a `#extension` directive is needed to enable them before `#version 450`?