[423051] Fix the plugins' branding and copyright

* Externalize %pluginName & %providerName
* Add the missing about.html files

Change-Id: I76102288cd3ac92c8b7cdd77d4fa228c71d71a06
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>
[422478] Fix a migration issue from Viewpoint 6.9.x to Sirius 0.9

The DiagramRepresentationsFileMigrationParticipant MIGRATION_VERSION still refers to the 6.9.0 version while a new one has been added (7.0.0). 
So the 7.0.0 migration is not called for someone migrating from Viewpoint 6.9 to Sirius 0.9.

Change-Id: Id3f70ac85716be245fb1f5f4af1b192ea135f068
[426691] Remove obsolete classes linked to the old "Designer Session
View"
Change-Id: I126aec0d61e67066b6b2bc41268206c0425ef70a
Merge "[426691] Remove obsolete classes linked to the old "Designer Session View" Change-Id: I126aec0d61e67066b6b2bc41268206c0425ef70a"
[426691] Move from
org.eclipse.sirius.ui.tools.internal.views.sessionview classes still
used in the current UI.

Change-Id: I23d8cb1ec6aed8f002efa33a4bef26bcc690756f
[426691] Move from the sessionview.extension package some extensions
which are not specific to the designer session view

Change-Id: I83cab2f7fb0f99d47680f9b5bd8716988d63cf7d
[426439] add a new migration participant which adds a HideLabelFilter
when it's missing.

Change-Id: I7c8fb1d9695e1a03081dbf8e618c0b0714959ff6
[426995] Only call doAddSemanticResource once

Change-Id: Ie2f29e377f60a84023baad8c22f66712112b2d25
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>
[424609] Move the Sirius perspective classes and declaration from
org.eclipse.sirius.ui to org.eclipse.sirius.editor.

Change-Id: I41053801c2a7e9330f428675f9fb6a2f48042415
[cleanup] Reference the correct feature in the error entry 

Change-Id: Ib628617e26feacc0fb30bc6076edaeb137035f5a
Signed-off-by: Maxime PORHEL <maxime.porhel@obeo.fr>
Optimize the sizes of our PNG files

Use pngcrush to optimize our PNG files. Command-line used:

  find . -name "*.png" | while read f; do pngcrush -q "$f" "${f}.new" && mv "${f}.new" "$f"; done

In the source tree, this gets from 29M of PNG to 13M. The size reduction
is less spectacular in the built version, but still not negligeable: the
complete update-site gets from 44M to 39M

Change-Id: Iec5d8b379631547765045f3033cc7df398c5839c
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>