Provide UV Offset Values as a per-Texture Material Property

[ilexp]

Summary

As described here, there is currently no easy and convenient way to assign a UV offset to a texture.

Analysis

• While this could be done as a per-Renderer property that adjusts vertex generation, a preferable way seems to be having an additional Material property per-Texture. (Multitexturing, shared among different renderers, etc.)
• This could be achieved by providing the appropriate uniforms in the default shader and evaluating them during vertex processing.
• For custom shader support, this feature should also be provided as part of a potential shared "shader library".
• With regard to this, issues #219 and #220 are closely related.

[ilexp]

Issue:

• With offset and tiling values being a Material property, something that could be easily batched as part of vertex data suddenly becomes its own drawcall. This is not ideal performance-wise.
• Determine whether this is relevant.
• Note: Checked with Unity for reference, and it appears they go the uniform value road. Still, not sure on this.

[ilexp]

Closing this. Doesn't seem to provide a benefit large enough to account for the increase in maintenance and complexity.