figure out issue with neighbours API

[Kalyan Dutia]

we're getting a 404 which is raised when the request entity isn't its own neighbour in /neighbours. This problem seems difficult to reproduce locally. I've temporarily disabled the 404 on the EC2 machine and it seems to work.

Also, the neighbours column of the metadata explorer could fail more gracefully, rather than bringing the whole UI down with Internal Server Error

example entity: http://www.wikidata.org/entity/Q836805