Automatically build mobile menus from navigation, and clean up external ProfileMenu API

Summary:
Depends on D20355. Ref T13275. Ref T13247. Currently, "Hamburger" menus are not automatically built from navigation menus. However, this is (I'm almost completely sure?) a reasonable and appropriate default behavior, and saves us some code around profile menus.

With this rule in place, we can remove setApplicationMenu() and getApplicationMenu() from StandardPageView, since they have no callers.

This also updates a lot of profile menu callsites to a new API which is added in the next change.

Test Plan: See the next two changes.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13275, T13247

Differential Revision: https://secure.phabricator.com/D20356