ctkDICOMQueryRetrieveWidget::getServerParameters() definition added back

The last commit on this file removed the definition of this function,
but left its declaration in the header file what caused linker error
with MITK that requires this function.
Merge pull request #486 from espakm/ctkDICOMQueryRetrieveWidget-fix

ctkDICOMQueryRetrieveWidget::getServerParameters() definition added back