WebGLRenderer: Convert to power of two textures that require it instead of giving wrap/minFilter warnings.

This reverts commit 46d0293c.

WebGLRenderer: Tweaked drawRange/groups handling. As per @WestLangley suggestion in 06893919.

@nraynaud do you mind double checking that I didn't break anything?

support WEBGL_color_buffer_float and EXT_color_buffer_half_float
also fixed a cleanup bug were the function would exit leaving the wrong buffer bound

Added call to _renderer.resetGLState() at the end of light loop in WebGLShadowMap.render(), updated WebGLRenderer.refreshUniformsShadow() to send inverse of point light position to shader. Fixes #7260.

Green refactor of Render-to-texture: Use a Texture instance inside WebGLRenderTarget rather than duplicating all internal texture fields.