CORAL-138: use WeakReference tagged with Entity id to be able to act
upon that information after actual Entity has been garbage collected.
CORAL-139: fix for a problem with setting db_table for classes don't
have one defined yet.
CYKLO-990: comparators based on an arbitrary resource attribute, or a
sequence of them
BAZYNGO-1457: factored out Direction enum
BAZYNGO-1457: Factored out PropertyBasedComparator as a generalization
of AttributeComparator
BAZYNGO-1457: MultiAttributeComparator needs specification of direction
for each of the specified attributes. Also factored out
CompositeComparator concept.
BAZYNGO-1457: moved general comparators to ledge-web
Merge branch 'dev' for release 1.0.19
release 1.0.19