Adds some of the UI components to allow us to visually render settings.
These are UI only and are not functional yet (@maxdeviant will be
working on these when he is back.)
You can see some examples by running `script/storybook setting`.
Release Notes:
- N/A
This PR cleans up a number of references in doc comments in the `ui` and
`theme` crates so that `rustdoc` will link and display them correctly.
Release Notes:
- N/A
