Refactor query() action to use GremlinGroovyScriptEngine

[aschrijver]

Using the script engine would provide more features (e.g. executing Groovy code) with regards to querying than the current straight-forward query compilation.

See: https://github.com/tinkerpop/gremlin/wiki/Using-Gremlin-through-Java#using-jsr-223-gremlingroovyscriptengine

As suggested by Amit Kumar in this post on the Vert.x google group: https://groups.google.com/d/msg/vertx/eIjzdQI23ss/hjYUtJcxVKcJ