Additional texture export options

1. Add options for different resolutions for specific textures.
2. Allow for custom sufix/prefix withouth having to create new output template.

Our game engine uses additional maps to run sheen/sss ect. We have set up the custom user channels to paint these maps.
However, to save memory, we dont need these maps exported out at the same resolution as the base maps.
It would be nice to be able to specify a different export resolution per texture the same way you can specify a file type and bit depth.  Also having options of 1/2, 1/4 or Double the texture set size as well as specific resolutions might help too.

Being able to add a prefix or sufix without having to make a new output template or changing the material name or manually changing the file name would be helpful when making variations.  If we exported our textures but also wanted a clean version without the dirt for example we could just add a simple _clean prefix without having to search through an extensive list of output templates.