Revamp of background again.

Switched from gradients to specifying two colors, updated shader to lerp between colors (Old shader still exists, renamed), added 3 more sectors, updated Nebula Highlights to be a separate texture, and removed old gradients.

Also created new Pair class to essentially emulate the Tuple generic.
Since generics cannot be serialized (displayed in inspector) I have created other class (TexturePair, ColorPair) that allow for this.  If more are needed follow their pattern.

Pair is used in the new background code if you need an example.