Add Dendrogram Visual

A dendrogram will now pop-up after clustering. The plan is to have a
setting that allows the user to select what visualization they are
wanting.
Add GraphicVisualizer Class

GraphicVisualizer will handling displaying the results of the
clustering.
Fix Class in Document ARFF

The nominal value for class is not set, so the class value is just a
string and can be anything for the Cranfield collection. This is not the
intention. All instances should have the class "cranfield".
Add Graphic Options in the Clustering Manager

The user will be able to determine if a 2D graph and/or dendrogram will
pop-up with the clustering results.
The Collection Percent Spinner Increments by 5
Add Reuters Collection

The parsing for the Reuters collection uses the Java SAX XML parser.
ReutersParser overrides the needed functions to properly parse the
collection. This parser only parses the Reuters collection in XML format
and will not parse the SGML format collection.

Also, I experimented with not using a class for the Cranfield collection
to test if it can be an option for the Reuters collection. The tests
were successful so I left the Cranfield collection without a class.

TODO: Each document in the Reuters collection either can have zero, one,
or many topics. I had trouble finding a way to give an instance more
that one topic, so the Reuters dataset will do without till that is
figured out. These can be used for classes in the future. The
getTopics() method in DocumentManager reads the lists of valid topics in
from a file in the collection directory.