Surfaces are selected by using ComboBoxes now
- changed to ComboBoxes in ui
- created and implemented Signals and Slots for ComboBoxes
- removed onSelectionChanged and moved functionality to slots of ComboBoxes
- use checkBox for mirroring and created slot (no functionality yet)
- renamed Qt variables to match mitk Style Guide
Signed-off-by: Hellena Hempe <h.hempe@dkfz-heidelberg.de>