Redesign of ImportView
Added Builder Pattern to PDFStudentList.
Added two new attributes:
 - returnList
 - lendingList
Added pdf test for dunning.
Removed public constructors of PDFStudentList
Removed old PDFStudentList creation in other classes.
Removed unnecessary null-check.
Added state for providing information for a single teaching material
Added an action for fetching a single teaching material
Refactored upload receiver into the import view
Put input stream from the upload to csv reader
Added returnList and lendingList to addContent
Deleted CSVUploader
Deleted unnecessary CSVHandler method.
Changed CSVTest due to changes of the CSVHandler api.
Zugriff auf alle nicht erhaltenen BorrowedMaterials implementiert
Persistierung des Eltern-Objekts wieder einkommentiert.
Merge pull request #197 from davvitt/issue#194-getUnreceivedBM

Zugriff auf alle nicht erhaltenen BorrowedMaterials implementiert
Removed createParentObjectsFromCSV.
Parent objects are created together with student objects now since all
parent information are in the same csv as the student information.
Added categories and categoriesInfo state
Deleted test method that tested the creation of parent objects.