This should "fix" all the problems of textures not rendering when the first instance of the geometry rendered didn't use.
Yet another premature optimisation that created a lot of confusion :(

resolves #5058

webgl_sandbox goes from ~30.000 to ~7.000 calls.

This is consistent with usage of needsUpdate throughout the rest of the
code. The property is not added to all uniforms for now, so the check
needs to be needsUpdate === false rather than just ! needsUpdate.

Also cache uniform locations in the uniformsList, so that querying them
from the program is not needed. This reduces CPU usage.

After this change, if 'clean' property is added to an uniform and
evaluates to true, the uniform is not uploaded to the GPU. This is used
to avoid needlessly refreshing lights uniforms when the material changes
but the program does not, saving CPU usage.

This saves redundantly setting some uniforms when changing materials that
share the same program, reducing CPU usage. This can give a significant
performance boost on devices which have a higher-performance GPU compared
to the CPU, such as Tegra K1.

More precision is used for the green channel in RGB565 and DXT texture formats, so this would improve the quality in those cases.