Update gulp dev task to no longer build scripts
Rename gRex class into Client
Add GremlinFunction and GremlinStep classes

- Remove Gremlin.appendMain()
Add IdxGremlinFunction class
Fix IdxGremlinFunction not properly inheriting from GremlinFunction
Add CollectionAccessor class. Remove Gremlin.appendIndex().
Add CollectionStep class. Remove Gremlin.appendCollection().
Add PipesStep class. Remove Gremlin.appendPipes().
Argument classes are no longer aware of client options
Move object classes and function classes to their own respective folders
Fix client creation test
Merge branch 'refactor-gremlin' into develop
Update local version of gulp
Distinguish GremlinMethod class from GremlinFunction class
Make Gremlin._ a GremlinFunction
Move Gremlin object and function files to /gremlin
Move Pipeline steps to /steps folder
Move Graph.idx Class to /graph folder
Use callback api in tests
Simplify handling of options in grex.connect()