[427803] Extract diagram default tools in a DiagramEnvironment.xmi

Pin/Unpin actions are now in the diagram.ui plugin and ToolGroup is a
diagram specific tool: these default tools are now declared in the
diagram.ui plugin.
Palette manager now gets its default tools from both core and diagram
environments.
The core Environment.xmi does not currently provide default tools.
Update the URI query to be able to detect all environment files.
Declare an uri mapping to register DiagramEnvironment.xmi as a Sirius
environment file.

Change-Id: I4446a921e6128b873ffa165dea8256460401cd3d
Signed-off-by: Maxime PORHEL <maxime.porhel@obeo.fr>
[cleanup] Remove useless internal class AbstractSessionCloseListener

Replace its two usages by references to its equivalent superclass,
SessionManagerListener.Stub.

Change-Id: I9f6e9b76dd8968d7104d31ed14a0a8ef20ba3ad9
[cleanup] Remove dead code in ITreeCommandFactory

Change-Id: Ib937cde27d1c5f8bde239e1ea09eb68b0b5c4fb4
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>
[cleanup] Fix core interpreters' description messages

Change-Id: I4c1ebcd7de41fffa5c419cfeb21bd0045a47dfa0
[431359] Avoid NPE when the factory for aird files is not registered

This is an emergency workaround until the real issue can be addresses
properly.

Bug: 431359
Change-Id: I00ab7264c710ed108e966d97c8d21403095f56f6
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>