Support lambdas in Gremlin.Net

Gremlin.Net should support lambdas. We already discussed this in the pull request for TINKERPOP-1752. Here is what spmallette said over there:

Any reason we don't support lambdas? Even if .NET can't support them natively for some reason wouldn't we minimally support the ability to pass a python/groovy/etc lambda? it's kinda weird that way, but i think back to the point that kuppitz made on the dev list the other day where he stated that he doesn't always find a way out of using lambdas in production systems he works on - so ultimately users will need that kind of capability i think.

C# lambdas would require some kind of C# parser on the server side, so at least in the beginning a way to send lambdas from already supported languages in Gremlin.Net should be enough.