Support literal property values for Sparql visualization options

[michaelnchin]

Issue #, if available: #294

Description of changes:

• Allow use of node property values with SPARQL --group-by/--display-property/--tooltip-property visualization options.
• Change default node group from value of binding type -> value of *:type property (if available). Group-by-label will also now use the *:type property value as the node class identifier.

The P. prefix must be added to the property name to signify that we want to look in the node property map, Ex.

rdf:type-> P.rdf:type.

Previously, these options would only search within the subject node binding itself. Specifying a property without the P. indicator will continue to limit the property search to the binding.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.