ESCKAN-75 Fix nerves filtering

[dvcorreia]

Current changes:

• Each time we select a connection, in the context provider, it filters out anatomical entities that are not present in the neurons file provided by the client. This is propagated through the app, reflecting both in the PDF download and connections summary.

Another solution for this can be seen in develop...feature/ESCKAN-75.

[dvcorreia]

@ddelpiano changing this in the context provided may very well mess with something that I'm not aware in the application. I've read a bit of the code where it deals with the vias anatomical_entities, but I don't get a lot of the business logic, so I don't really get it. If this changes don't make sense, please let me know :)

[ddelpiano]

lgtm