Cypher API mapping

The Python client uses Python objects and types as interfaces for GDS methods:
- The graph object can be used to inspect graphs from the GDS graph catalog.
- The model object can be used to inspect models from the GDS model catalog.
These objects are used in place of name strings in procedures and functions that take a graph or a model as an input.
Pipeline objects can be used to configure and use machine learning pipelines.
Method calls corresponding to Cypher procedures (preceded by CALL in the docs) return:
- A table as a Pandas DataFrame, if the procedure uses the stream mode.
- A method-specific return type for anything else (for example algorithms in stats or mutate mode).
gds.server_version() returns a ServerVersion object.