Update rml_generator_lib.py with SPHN Connector latest changes (depth 4 handling)

@663783507196 When you have some time it would be great if you could double-check that these changes do not have any unexpected effects on the queries generated for non-connector case. The methods get_restrictions has some new changes and this is used by query_functions.py. Methods get_range, check_invokation, get_supporting_concepts, get_target_concepts, and get_restrictions_map_with_range should not be used.