CMS UI refresh

This was originally released as CMS UI 11.21.0. Due to unintended semantic breaking changes, we have removed CMS UI 11.21.0 from nuget and will re-release in the future with some additional bug fixes. We suggest downgrading to CMS UI 11.20.x for now. Thank you for your feedback and patience. :)

We are introducing a refreshed editor interface in a future release, here is a preview. The new navigation menu is functionally different from its predecessor, but the changes outside of the navigation are purely cosmetic. In order to prevent breaking changes, the new navigation will not automatically replace the old global menu in custom implementations, such as in add-ons; code changes will be required if an add-on wants to use the new navigation instead.

Our first change was to completely redesign CMS UI navigation. This modern navigation takes up less screen space by moving product navigation into a waffle menu in the top left that opens a drawer. 

Once the new navigation was in place, there was a very noticeable stylistic difference between the navigation and the old UI. We set out to bring the UI more in sync with the navigation. To accomplish this, we modified the colors, flattened buttons, removed some dividers for a cleaner look and feel, and changed the font. 

Before and after comparisions: