Refactor "unconfirm" functionality into a gem.

- Rename maybe_confirm => unconfirm.
- Add ApplicationHelper to handle session updates.
- Add view helper and accompanying specs.
- Refactor confirmation javascript into a jQuery plugin.
- Add a view helper to generate the unconfirm settings
  and call to the new jQuery plugin.
- Add view and asset pipeline initializer.
- Fix JS bugs and other bugs.