Split code for special variables to a new method
Correctly use display name instead of userid

Fix #70
Split parameter methods into a new class
FIx unit tests
Use switch instead of if/elseif
Reduce complexity of prepareFileParam()
Merge branch 'issue/70'

* issue/70:
  Reduce complexity of prepareFileParam()
  Use switch instead of if/elseif
  FIx unit tests
  Split parameter methods into a new class
  Correctly use display name instead of userid
  Split code for special variables to a new method