[BUG FIX][Measurement] "Fixed sized circle/double ellipse" checkbox active when no data selected

Summary:
In the 'CreateQtPartControl()' function (in the QmitkMeasurementView.cpp) file I added the setEnabled() function (d->m_FixedParameterBox->setEnabled(false);) to the corresponding QGroupBox (m_FixedParameterBox).
I also made the needed changes in the OnCurrentSelectionChanged() function to enable / disable the element if data is loaded / unloaded.

fixes T28786

Test Plan:
manually tested:

1. Open mitk workbench
2. Open the "Measurement" plugin

The "Fixed sized circle/double ellipse" checkbox (QGroupBox) can only be checked if data is loaded

Reviewers: kalali, O1 MITK Reviewer Group I, kislinsk

Reviewed By: O1 MITK Reviewer Group I, kislinsk

Subscribers: kislinsk, kalali, m907r

Maniphest Tasks: T28786

Differential Revision: https://phabricator.mitk.org/D578