UI Updates: New Home Page and My Collections Overlays

New Home Page and My Collections overlays to completely replace existing
"start page" system per
https://trello.com/c/CUGQrodT/147-home-page-my-collections-overlay-general-ui,
https://trello.com/c/86b7wBek/189-home-page-overlay-specifics,
https://trello.com/c/Gcwk89yj/190-my-collections-overlay-specifics and
https://trello.com/c/4xrxKnLq/185-selection-of-new-featured-collections-list.
Final background color and featured item list TBD. Note: This check-in
includes all of the new functionality in a test menu but the old "start
page" overlays are still in place. Therefore this version is for testing
only, and should not be deployed to production without further changes
(removing of old "start page" system.)