ENH: Add option for script directory in SLICER_ADD_PYTHON_TEST macro

The default is still CMAKE_CURRENT_SOURCE_DIR.
BUG: Fix slice view bug in the addition of the qMRMLLayoutViewFactory

The factorization gave the slice view change the name given to the slice
view (no longer the same as their layout name). For example, the editor
was not working anymore due to this.
This is fixed by re-setting the slice node's name to their layout name.