Fixed spelling in isAssigned... method
Updated xtext to 2.7.2, zest to 1.5.101, removed svn
Cleaned up property view's content provider and label providers.  Now
uses an ILazyTreeContentProvider instead of an
ILazyTreePathContentProvider.  Also modified the internal structure of
the tree.
In the property view, do not aquire a lock when access the property
lookup job.  This is no longer necessary since the model listener was
removed.
Icon updates for use by the graphical editor.