LOW / it is now possible to push to palette elements from the view
modeler. However as the palette is fixed, just add a possibility to
place it by setting coordonates. This should be changed later, one would
prefer to move directly the elements inside the palette, but fits for
the first iteration of PRI
MEDIUM / When the user create a link from a shape to nothing, the system
ask for possible relationship associated with the source shape
corresponding edition pattern. Then, a new shape/edition pattern is
created and a link to. The condition is that a link schem must exist and
a drop schem as well for the target shape/editionpattern. This is one of
the PRI's requirements.