Gradients not handled in contrast form

[ewainberg]

Add logic (and frontend functionality) to process and fix gradient contrast on a per-color basis

[ewainberg]

Gradients also treated as background-images, so they get flagged for "Images Should Have Alternative Text". Must fix.

[ewainberg]

There is also another big issue which will be fixed with this, but... yeah. When fixing contrast issues, if a child element doesn't have the background set within itself (i.e. it is set on an parent or grandparent element), it will fall back to default colors. This is not desired behavior