Implement pre-CTE filtering

[JackAtOmenApps]

Add the ability to filter down prior to running CTE.

For instance, in a graph of a municipal district, it may be more efficient to limit the search to a particular region, category of nodes/edges, or other characteristics.

This would involve modifying the raw Postgresql statement to include the additional filtering.

[JackAtOmenApps]

Options to pre-filter on the following:

• [X] A queryset of node instances to ignore
• [ ] A queryset of node instances to require
• [ ] A queryset of edge instances to ignore
• [ ] A queryset of edge instances to require
• [ ] A ForeignKey on the node model
• [X] A ForeignKey on the edge model

Maybe in the future:

• [ ] A ManyToManyField on the node model
• [ ] A ManyToManyField on the edge model