Auto-complete function signatures - Part 1

@Benglin - I have split up PR: https://github.com/DynamoDS/Dynamo/pull/2688 into smaller PR's, of which this is the first. 
Again, documentation and example would help a great deal. If as a reviewer I do not care about your work, I would have looked at these lines and go "ah, I think these C# codes run fine, pass". Then I won't be doing a reasonable job as a reviewer ;)