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.
Seeds for roles :material and :shipper
Access control, corrections and tests for shipments and related changes