Move the action menus, DnD uploads and onbeforeunload to ReviewRequestEditorView.

The code from reviews.js for handling the menus, initializing the
DnDUploader and prompting on page change while there are pending edits
have been moved into ReviewRequestEditorView.

The action-related code has been consolidated into a _setupActions
function.

Tested the menu items in the menus, and that menus opened.

Tested that I could drag-and-drop files into the review request.

Tested that I was warned when trying to leave the page when I had a pending edit.