JBIDE-18001 Cherry picked PR #273 to avoid dragging in unrelated changes to eclipse metadata files
JBIDE-17808: Mechanism to define and detect "families" of IU

* Plugins can contribute a "family" definition (such as earlyaccess,
supported,
blacklisted...) which lists the various ius for the given family
* A utility class allows to do request to compare current installation
with families
* Central editor shows when Early Access content is installed (computed
from family)
* An installation page is added to report Early Access IUs
JBIDE-18024 - Ensure copyrights and provider names are correct