Make dialogs a little easier to use

Summary:
  - Dialog pages currently have no titles or crumbs, and look shoddy. Add titles and crumbs.
  - Dialog titles aren't always great for crumbs, add an optional "short title" for crumbs.
  - `AphrontDialogResponse` is pure boilerplate. Allow controllers to just return a `DialogView` instead and get the same effect.
  - Building dialogs requires a bit of boilerplate, and we generally construct them with no explicit `"action"`, which has some issues with T4593. Provide a convenience method to set the viewer and get a reasonable, explict submit URI.

Test Plan:
  - Viewed dialog on its own.
  - Viewed dialog as a dialog.

{F132353}

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D8577