http://bugs.mitk.org/show_bug.cgi?id=16770

- The number of time steps between masks and images can now be different
- If the mask does not have the selected time step, its last time step is used instead
- The used mask time step is displayed in the mask label
- The statistics are now updated when the time step changes
- If the mask is empty, the displayed statistics values are set to 0 (was displaying uninitialized variable values)