R1:419b7ceebb0f

Move inline comment actions into a dropdown menu

Summary: Ref T11401. Ref T13513. This paves the way for more comment actions, particularly an edit-after-submit action.

Test Plan: Took all actions from menus, via mouse and via keyboard (where applicable).

Maniphest Tasks: T13513, T11401

Differential Revision: https://secure.phabricator.com/D21244