Allow profile menu items to be locked to the top or bottom of the menu

Summary:
Depends on D20353. Ref T13275. This is just some small quality-of-life fixes:

• When you add items to menus, they currently go below the "Edit Menu/Manage Menu" links by default. This isn't a very good place for them. Instead, lock "edit" items to the bottom of the menu.
• Lock profile pictures to the top of the menu. This just simplifies things a little.
• Show more iconography hints on the "edit menu items" UI.
• Add a "drag stuff to do things" hint if some stuff can be dragged.

Test Plan:

• Added new items to a Portal, they didn't go to the very bottom. Instead, they went above the "Edit/Manage" links; a sensible place for them.
• Viewed the "edit menu items" screen, saw more hints and visual richness.
• Viewed/edited Home, Projects, Portals, Favorites

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13275

Differential Revision: https://secure.phabricator.com/D20355