Merge in the org.eclipse.xsd Git repository

Reuse JustJ's update site generator for promotion of builds.
Provide a Jenkinsfile to prepare for a multi-branch pipeline job.
Stop building pack200 artifacts.
Use https for download.itemis.com.
Include the root of the repository as a project.

https://gitlab.eclipse.org/eclipsefdn/emo-team/emo/-/issues/430

Change-Id: Ibe27c53175bcbaa66c693f6b4db8299a39185e0f
Signed-off-by: Ed Merks <ed.merks@gmail.com>