KUI Sass Variables Refactor

[snide]

Describe the feature:

KUI has some inconsistencies with namespacing and global variables that lead to variances in our colors, spacing, theming and fonts. I'd like to try and attack the following as a means to get it more consumable for development.

• Proper variable scoping ($global vs. $component) [UI Framework] KUI sass variable namespacing / rework #11033
• Consolidate the color palette into some core colors.
• Consolidate our font-sizing and weights to some defined options.
• Consolidate our spacing and padding to some defined options.
• Consolidate our border usage to some defined options.
• Consolidate our box-shadows to some defined options.
• Remove any variable bleed (named variables that aren't global that are used in multiple components).
• Use a mixin system for declaring BEM namespacing to avoid cascade / naming errors.

Likely this will take several PRs in parts, so attaching it to the meta tag. cc @cjcenizal who I've talked a bit about with this.