Add smoothing options to textures

[BenjaminDRichards]

Spinning off the BitmapText plugin, it would be nice to have a smoothing toggle. We specialize in sprite graphics, which automatically has some retro appeal. Retro doesn't look too great when scaled up, though: LINEAR interpolation smooths things out.

A smoothing toggle could set NEAREST interpolation on textures, giving us much sharper retro styles.

Note: This would also have to be implemented in canvas rendering options, which don't have much to do with WebGL texture wrappers for some reason.