Vessel Extraction Step:

Mostly empty for now.
Fix comboboxes sizing.

The comboboxes on the same row as save button or open folders are enlarged
beacause of the icon size. It causes a displeasing discrepancy in the
display.
Add choice of registration type

Add a combobox for the user to choose the registation type in advanced mode
Automatically guess registered image pixel type

The BrainsFit module allow the user to choose the output registered image
pixel type. By default it is float.
To be more transparent, the output image pixel type is now guessed based on
the input moving image type.
Shorten output volume suffixes

After adding numerous suffixes to the output, the names start to grow a bit
too much. Shortening the suffixes will help that.
Update slice views function

For clarity and convinience for the user, the slice views are updated when
the modules has finished.
Plug memory leak

The ctkWorkflow didn't have any parent causing it to linger around with
its steps after closing the application. Adding the parent of the module
fixes this.