Add very basic "quick create" menu

Summary:
Ref T3623. This is like a pre-v0, in that it doesn't have a dropdown yet.

Clicking the button takes you to a page which can serve as a right click / mobile / edit target in the long run, but is obviously not great for desktop use. I'll add the dropdown in the next iteration.

Test Plan: {F105631}

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Maniphest Tasks: T3623

Differential Revision: https://secure.phabricator.com/D8088