[439871] Setup the CI-build with a specific headless profile

The specific headless profile expects a
sirius_$PLATFORM_minimal_headless.target file in the 
org.eclipse.sirius.targets project.

Bug: 439871
Change-Id: If613ad7e1a51b6a76554404c8ce9238c955474d7
Signed-off-by: Cedric Brun <cedric.brun@obeo.fr>
[439871] Remove UI dependencies which are not used *from the code*

Bug: 439871
Change-Id: I69dcb3546c3da1c4a4d2b15509b9e866c32aaabb
Signed-off-by: Cedric Brun <cedric.brun@obeo.fr>
[439871] Stop using LabelProvider the Table dialect

EMF introduced IItemLabelProvider exactly for this need: to avoid 
depending on UI stuffs just to retrieve a label. This commit makes the
refresh use directly the IItemLabelProvider instead of wrapping it into
a useless labelprovider.

Bug: 439871
Change-Id: I75ecf4081cc50243ee3ce90276f9cae8ed1a4130
Signed-off-by: Cedric Brun <cedric.brun@obeo.fr>
[439871] Add a default SelectorProvider

This provider is available when nothing else is contributed so that
the corresponding code will work nonetheless, but it is expected to be 
overrided by the one in diagram.ui.

Bug: 439871
Change-Id: Id8631a36aac090f8a786b590a2c364c6adccc23c
Signed-off-by: Cedric Brun <cedric.brun@obeo.fr>
[439871] Move the diagram refresh logic down to the non.ui plugin

Move the DiagramDialect and all the code it depends on in the non.ui
plugin.

Extract the ViewpointSelectionCallback logic in a dedicated class lower
in the stack (not in the UI) and delegating from the old one.

It is not compiling, we still have a reference to a
canonicalsynchronizerImpl and some logic to capture SWT line height.

Bug: 439871
Change-Id: I06f70d0264231ef364163f42cfbb49d2e6055bdb
Signed-off-by: Cedric Brun <cedric.brun@obeo.fr>
[439871] Use CanonicalSynchronizer to hook diagram header computation

This commit adapt the CanonicalSynchronizer API so that it wrapps the 
computation of the diagram header (which can only be done with an UI).

Bug: 439871
Change-Id: I6250c5a628f76c4d038cf248851b1e06c01a0534
Signed-off-by: Cedric Brun <cedric.brun@obeo.fr>
[439871] Add extension pt to call the diagram.ui CanonicalSynchronizer

With this commit the CanonicalSynchronizer is called again when present.

Bug: 439871
Change-Id: Ic984c9dbba3208a0afb11820f1c05fc6e3756aaa
Signed-off-by: Cedric Brun <cedric.brun@obeo.fr>