Initial Stats data and widgets

[zwelz3]

When processing/loading RDF data, it is often informative to have basic stats on the data itself (e.g. # of triples). This ticket scopes in the development of a basic statistics class where stats are driven/exposed by queries and stored in basic tables. Basic stats may include:

stat	#
triples	123
subjects	34
predicates	12
objects	45
prefixes	3

Stats would be pluggable, e.g. we may have an OWLStats class that understands how to query for e.g. ObjectProperty Axioms.