Shipments, refactoring of HasState and strong params

 * IMPORTANT: tests for the new functionality are still missing!!
 * New type of state machine: shipment (for booth boxes and similar)
 * New roles to support the shipment workflow
 * Strong parameters instead of protected_attributes
 * Refactoring of HasState, moving more and more logic into the concern
 * State machines (Request, Reimbursement, Shipment) can only be edited by the
   requester and only in initial state. Added additional actions to support
   setting the approved amount and similar actions.

Conflicts:
	app/models/user_role.rb
	config/locales/models.en.yml
	db/schema.rb