Add file-type configuration property to rexster.xml

Set file type for example graphs 1 and 2 to GraphSON and replace java serialization and GraphML files.
Add FileType to Mock tinkergraph.
Drop the properties element from TinkerGraph.

Convert to graph-storage at the root of the configuration tree as there won't be many more "properties" for TinkerGraph.
More complex traversal performance tests.
Add more traversal tests and do one RexsterClient per thread.