Port to TinkerPop3

This is a major change to update the gremlin-node package to use TinkerPop 3.
TinkerPop 3 is not backwards compatible to TinkerPop 2. As such, this repo/fork of
gremlin-node has been renamed to gremlin-v3. Likewise this repo will become the source
repo for a new NPM package gremlin-v3

Many changesare made in this commit to make unit tests pass, but more changes
should be made to clean up the result. For example, the fundamental
concept of a 'pipeline' in TP2 changed to a 'traversal' in TP3,
but this revision still uses the term Pipeline extensively in the
code.