Core: added application modifying helpers.
Schema: added basic entity manipulation logic.
Schema: added basic entity relations manipulation logic.
Refactoring: simplified normalization of schema-related identifiers.
Core: added dependency on Passenger for application reloading.
Rails: worked around loading of Rabi::Entity::Attribute.
UI: added RailsAdmin for data manipulation & schema configuration.
Schema: added constraints for entity attributes (presence & enumeration).
Auth: added users & access control management.
Fixed `Rabi::Relation.new`.
Fixed `User#name` when e-mail is absent.
Fixed loading of overridden models.
Fixed handling of complex User::Permit subject with RailsAdmin.