R1:d8713f6f0b8c

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.