* Add session option to Rememberer class
* Update session login function to allow send additional data
* Add Remember me checkbox
* Cleanup login modal
- Use Symfony's Session component to work with sessions, instead of a custom database model. Separate the concept of access tokens from sessions once again.
- Extract common session/remember cookie logic into SessionAuthenticator and Rememberer classes.
- Extract AuthenticateUserTrait into a new AuthenticationResponseFactory class.
- Fix forgot password process.
- Use cookies + CSRF token for API authentication in the default client. This mitigates potential XSS attacks by making the token unavailable to JavaScript. The Authorization header is still supported, but not used by default.
- Make sensitive/destructive actions (editing a user, permanently deleting anything, visiting the admin CP) require the user to re-enter their password if they haven't entered it in the last 30 minutes.
- Refactor and clean up the authentication middleware.
- Add an `onhide` hook to the Modal component. (+1 squashed commit)
