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. 
These comments seemed to be outdated, for example, I am not sure what ```functionName``` and ```functionPrefix``` will be. Another way to help with review is to have appropriate documentation so I can understand the intents of this method without mentally executing the code, I hope that makes sense.

Also, since these are utility methods, we need test cases for them. I'm sure you already wrote some test cases, in which case you should include those test case in this PR so they can be merged in together.