GraphSONInputForrmat and GraphSONOutputFormat now support modes,
configurable via "faunus.graphson.mode"

Tested and worked for upgrading data from Titan 0.3.x to 0.4.x
using GraphSON extended via Faunus 0.3.x to generate output using "g._()"
and use Faunus 0.4.x to process the graphson generated by 0.3.x as the input.
(cherry picked from commit 8d2241f)