When picking a default menu item to render, don't pick disabled items

Summary:
Depends on D20358. Fixes T12871. After refactoring, we can now tell when a "storage" menu item generated only disabled "display" menu items, and not pick any of them as the default rendering.

This means that if you're looking at a portal/menu with several dashboards, but can't see some at the top, you'll get the first one you can see.

Also clean up a lot of minor issues with less-common states.

Test Plan:

• Created a portal with two private dashboards and a public dashboard.
• Viewed it as another user, saw the default view show the dashboard I can actually see.
• Minor fix: Disabled and enabled the hard-coded "Home" item, now worked cleanly with the right menu state.
• Minor fix: added a motivator panel.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T12871

Differential Revision: https://secure.phabricator.com/D20359