Add conformance tests for TEXTURE_BASE_LEVEL and TEXTURE_MAX_LEVEL.
Merge pull request #746 from dvander/mipmap-levels

Add conformance tests for TEXTURE_BASE_LEVEL and TEXTURE_MAX_LEVEL.
Add tests for WebGL2 non-POT texture support.
Exclude WebGL1 npot texture tests in WebGL2.
Merge pull request #743 from dvander/webgl2-non-pot

Add tests for WebGL2 non-POT texture support.