Improve masking of Flood filling effect #3
Description
Currently, flood filling can propagate in the entire image and the result is applied to the "editable area".
However, it would help if flood filling would only propagate in the "editable area" - it would make it easier to stop leaking by using an appropriate mask.
vtkImageThresholdConnectivity filter already has a stencil input, so we should just generate a stencil from the editable area and set it in the filter:
http://www.vtk.org/doc/release/6.3/html/classvtkImageThresholdConnectivity.html#a106f02553f3445161a9d742b9481dc14