Move package-visibility classes to internal packages

The Tycho tests were failling because the tests themselves are
doing illegal instantiations of instances using a constructor
which is not visible.
In particular : LayerEntry and GridCell

This commit
- introduce internal packages 
- isolates the classes which had a "package" visibility into 
these internal packages
- set x-friend export of these internal packages to the test plugin
- enables PDE tooling
Add about.html and update provider name
Add an Example tab in the gallery for Paperclips