[WIP] Remove persistance responsibility from CASinoCore

Background: rbCAS/CASinoCore#12

This is my "work in progress" branch for implementing a Pull Request to CASinoCore to address moving the persistance layer to [rbCAS/CASino][CASino] (and provide directions for non-Rails users)

This also pulls in my work from [dlindahl/CASinoCore/feature/use_activesupport_configuration](https://github.com/dlindahl/CASinoCore/commit/caf8d2db7ed4238293dd8f19b4be4ae77eedb2af) for reasons mentioned in the commit message.

* [ ] Add an "always available" configuration so that implementor classes can be stored someplace
* [ ] Remove all traces of self-contained persistance functionality (Rake tasks, `schema.rb`, etc)
* [ ] Provide common interface for ORM implementations
* [ ] Implement `LoginTicket` concern
* [ ] Implement `ProxyGrantingTicket` concern
* [ ] Implement `ProxyTicket` concern
* [ ] Implement `ServiceRule` concern
* [ ] Implement `ServiceTicket::SingleSignOutNotifier` concern
* [ ] Implement `TicketGrantingTicket` concern
* [ ] Implement `TwoFactorAuthentication` concern
* [ ] Implement `User` concern
* [ ] Implement `ValidationResult` concern
* [ ] Remove all traces of Rails integration. That belongs in the rbCAS/CASino gem
* [ ] Fork [rbCAS/CASino][CASino] and update integration points
* [ ] Fork [rbCAS/rbcas.github.com][docs] and update documentation

[CASino]: https://github.com/rbCAS/CASino
[docs]: https://github.com/rbCAS/rbcas.github.com