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.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

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