New naming scheme for theme roles + migrating some background colors.

[isoos]

• Deployed to staging for further verification.
• Started to separate named colors in an explicit way like smokeWhite and aliceBlue. These names are either from the HTML color names or if there is no such name, a widely used name is picked for it.
• Merged very similar colors into a single one, e.g. f8f8f8 and f8f9fa is both merged into f5f5f7. Fewer colors makes a more consistent color palette, and the contrast/separation between them is easier to review.
• Started to refactor and use names that first focus on their role neutral, inset, selected and then specify their property like bgColor or hover-bgColor. This makes it much easier to pick the appropriate variable when selecting colors for a component, e.g. selection or hovering should be consistent across the components this way.
• The PR is mostly for some of the background colors, but wanted to verify the naming style before spending much time on it.

[sigurdm]

Can we keep the colder highlight color?