Ruby: Add query for access paths in model editor

[koesie10]

This adds a simple query for creating a subset of valid access paths that can be used in MaD models. It's not intended to be complete, and will probably be rewritten to be a recursive query rather than this simple query.

Considerations:

• Right now, it's a simple query that hardcodes some strings, but it should be recursive in the future.
• In the future, it might make sense to make this a graph query (i.e. having nodes and edges query predicates), but we want to get this simple solution in first.
• Util::pathToNode does something close to what we want, but it doesn't have the details and defType, which are really useful to have in the model editor.
• The intention is to iterate on this query, so the most important part for now is that the query is at least correct in reporting valid access paths.

It seems like the query is also reporting Argument[self] for for example def self.self_foo. Does this make sense? It seems like the method node does return the parameter from getSelfParameter.