[553776] Consider the new JumpLink type from GMF Notation in GMF Runtime

This commit changes:
* the drawing of the figure in PolylineConnectionEx (make a "blank line"
  instead of classical jump)
* the property page in ConnectionAppearancePropertySection to correctly
  show the new property value

This commit also adapts some utility methods in LineSeg and
PointListUtilities to fix some bugs discovered during the tests.

Bug: 553776
Change-Id: I500f372e604589be6b395d9e3b478ba884043a22
Signed-off-by: Laurent Redor <laurent.redor@obeo.fr>