Added get methods to Property class
Fixed a small bug in per-level constraint resolution
Revert "Removed LEVEL token from Constraint grammar and updated references"
Slightly tweaked WorldTreeFactory to keep some newer changes

This reverts commit 24c2444a2f6aaf65304c3e52348fc4e03684b948.

Conflicts:
	src/internal/tree/WorldTreeFactory.java
Added small fix to solve NPE issues on WorldTree constraints
Working on PropertyDef materialization
Added get methods to PropertyDef class
Added Datum class and updated references