1059: Save a requisition

Short description: 

• Create a 'save' method in RequisitionController
  This method is responsible for calling the API that will update the requisition object, displaying a loading icon while the HTTP call is running, and finally displaying a success or error message. Ideally the requisition controller wouldn't directly call the API — this should be done in a Factory (that directly deals with the Requisition Service's APIs), but the current implementation doesn't have this — and this ticket should focus on user-facing technology.
• Add a semi-transparent toolbar with a 'save button' on it
  When clicked, this button will call the RequisitionController's save method. This save button is visible on the requisition view page.