A temp hot-fix for auto texture size optimize problem.

Added a checkbox called "Optimize texture size" when loading VRM models.

If checked, DDM will try to auto optimize texture size to save memory.

But in some cases, the texture will appear blur, for example loading a real human skin VRM model.

In that case you can uncheck texture size optimize, so you can get the full size texture without scale, as the original VRM model defines.