Make "Favorites" work more like other customizable menus

Summary:
Depends on D20373. Ref T13272. When you put Dashboards in Favorites, the render without a navigation menu, which is kind of weird.

Instead, make Favorites display a navigation menu. This effectively turns it into a weird cross between the home page and a portal, but so be it.

Also change the icon from "star" to "bookmark" since I think that a clearer hint about how it works.

Test Plan: Viewed dashboards in favorites, got a navigation menu. Edited items from portals, home, favorites.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13272

Differential Revision: https://secure.phabricator.com/D20374