lml/ost#347: Convert native confirm to dialog based confirm.

TODO:

* [x] Cache the settings at the session level.
* [x] Debug and fix the "Continue" button action.
* [ ] Make `maybe_confirm` JS seamless.
* [ ] Fix styles for checkbox and dialog.
* [ ] Add a simple page to view and change the settings.
* [ ] Refactor and extract it into a gem / plugin.

@jpslav/@dantemss: I don't particularly see a problem here.  But, http://railscasts.com/episodes/13-dangers-of-model-in-session?view=comments seems to suggest that this is not recommended.

Is it better to store the settings as a dictionary in session and then update with id instead?