visitor pattern in database

Added stubs of classes to implement the visitor pattern for database
access
Add an Element Visitor base class and implement an XML writter for. Added unit tests for the EVisitor and Element packages. More tests are needed.
XMLReader

EVisitorXMLReader.java basics written.
EVisitorTest class augmented to use reader
Merge remote-tracking branch 'origin/ched_database' into new_diagram

Conflicts:
	src/Element/Diagram.java
	src/Element/Element.java
	src/Element/ElementClass.java
	src/Element/ElementRelationship.java
	src/Element/ElementRelationshipAggregation.java
	src/Element/ElementRelationshipAssociation.java
	src/Element/ElementRelationshipDependency.java
	src/Element/ElementRelationshipGeneralization.java