ENH: slicer.util.VTKObservationMixin: removeObservers now accept no params

The method 'removeObservers' allows to easily remove all observers without
specifying all the method one by one.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23631 3bd1e089-480b-0410-8dfb-8563597acbee
COMP: Always set SOURCE_DIR variable for CLI modules

This commit will allow ResampleScalarVectorDWIVolume to be built
even if ResampleDTI is disabled.

This is needed because ResampleScalarVectorDWIVolume references
the source of ResampleDTI using the variable ResampleDTI_SOURCE_DIR

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23632 3bd1e089-480b-0410-8dfb-8563597acbee