First look issues:
- "New Segmentation Session" Widget is to small
- Group "Patient Image and Segmentation" to DataSelection
- Layer Button Group should be above the label selection
- The collapsible LabelSet Widget should be open (default)
- Extend text "Number of labels: #" with "Current Layer #"
- General functionality should be extract of the context menu of a label. Should be always selectable/visible (View/Hide all and Lock/Unlock all)
- "Deactiviating Tool"- Button is not needed