[444728] Avoid NPE if diagram or domain are null

If a DDiagram editor has a palette tool with a feature change listener
on a containment feature of DDiagram/DDiagramElement/Style (or one of
their super/sub types), and if the user deletes the current diagram, the
palette will be updated in post commit, and the null domain case has to
be handled as the gmf diagram is detached and the editor and its
PaletteToolFilterListenersManager are asynchronously closed/disposed. 

Bug: 444728
Change-Id: Ib92f85c3f1df8dc535fecdfe26a65a60241bbe23
Signed-off-by: Maxime PORHEL <maxime.porhel@obeo.fr>
[444759] Fix jump links status problem

If you enable the "specific default values" in connections preference
page and set it to "Rectilinear", all edges, created after that, have
the jump links set to "Above" instead of "None".

And also fix an activation problem at opening when the checkbox is checked (the combo is gray). This problem is here since the commit 9057209.

Bug: 444759
Change-Id: Idbaac8bf31bc93e149b9a535c07163fcf48e030b
Signed-off-by: Laurent Redor <laurent.redor@obeo.fr>
[441764] Remove unused images from the doc plug-in

Also rename some images were the URL in the textile and HTML was
"rebranded" from Viewpoint to Sirius but the file themselves were not,
which broke the refering page.

Bug: 441764
Change-Id: Iabf3db9d43b9af740dec68ffc236b3224db72f76
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>