implemented ActionHandler for import button in ImportView(Model)
added some testcode
added uploader for csv files
added test insertion
"Importieren" button
removed unneccessary method call
Worked on StudentPersistenceHandler
added leavingSchool to Student.Builder
persisting of students works now. 
removed error: gradeID has to be set manually, too.
Commit new ImportView
Merge pull request #136 from B3nRa/issue#78

Issue#78