Added notebooks covering node sets and different query methods

[joni-herttuainen]

Added two notebooks:
08_nodesets_and_node_queries.ipynb:

• node sets
• node queries

09_edge_queries.ipynb:

• edge queries
• memory optimization w/ iter_connections

[codecov-commenter]

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  Files           33        32    -1     
  Lines         2743      2706   -37     
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[mgeplf]

wow, this is really great; I think your idea of splitting the query by nodeset and query by node IDs makes sense.
Grammar and such, nothing jumped out, so after the split, LGTM.

[GianlucaFicarelli]

Well documented 👍

[mgeplf]

Very nice!