Add max_results to lookup

[cbizon]

@sierra-moxon would like to be do queries without ids. So: (chemical)-[treats]->(disease) to see what kinds of things might be returned. Usually in sql or cypher or something, you would run this exploratory query with a LIMIT 1 or something. So I think we want to add a limit like this to lookup.

We can currently get at a similar result by doing a lookup then a filter, but this will be far less efficient because you need to generate all the results and then pass to filter and the point here is to limit the overall runtime by returning as soon as you find the given number of results.