Fix regular expression matching in `query_networks`

[ianmkenney]

Since attributes of GufeTokenizables that are set to None are not explicitly stored in the Neo4j database, regular expression fails to match nodes. Because of this, we no longer introduce wildcards when a attribute pattern is set to None. Instead, we completely remove that attribute regex condition from the WHERE clause.

The test for the query_networks method was also changed so a network without a name is included.

Closes #273