Refactor 10226

This PR addresses important UX/UI areas to get moving forward with external contributors and Manager themers:

* refactors the Sass files to make it far easier to make radical Manager changes (color, contrast, general styling)
* refactors the overall layout templates to bring it inline with modern conventions
* fixes broken actions to restore manager functionality

This is likely not the final design—and there are plenty of items left to clean up—but it gets the ball rolling and certainly a solid starting point to do a test build for increasing community feedback and participation.