Sentry 3.0 (WIP) [Do Not Merge Yet]

## Notable Changes

- [x] Allow for custom hashing strategies.
- [x] Refactor permissions out into a driver-based system.
- [x] Refactor `*Provider` and `*Interface` implementations into single `*Repository` classes, stripping methods and simplifying where possible.
- [x] Multiple sessions.
- [x] Multiple login columns.
- [x] Inter-account throttling and improved DDoS protection.
- [x] Improved integration with Laravel (`Sentry::basic()`, easy email integration with queues).
- [x] Improved speed - make use of eager loading ~~and caching~~.
- [x] Allow use of implementations (such as Eloquent and Kohana ORM) to take place on the ORM level, without bloating Sentry with abstractions never used by Sentry.
- [x] Add support for two factor authentication.
- [x] Allow more flexible activation scenarios.