Simplify Mastodon

FEATURES:
* Centers content (puts posts into cards with space between them, dims actions until hover, hides title bar on scroll, puts left and right columns at edge of window)
* Puts compose and search on right, minimized to an icon unless in use
* Puts nav on left and minimizes to icons unless you hover
* Hides trends and nav items I don't think are useful (Local, Federated, Favorites, Bookmarks, and Lists) -- might add a way to expand or customize this in future

DISCLAIMERS:
* Works on top ~300 Mastodon servers (but it may not work on yours; I'm trying to find a better way to make this work on a product that could be on thousands of different domains)
* Does NOT currently do anything on the multiple column view (aka Advanced Web View)
* Does NOT currently do anything if your window is < 1175px wide (where the UI shifts)