This route was removed from the federation and doesn't exist anymore, so
checking for it doesn't make any sense.
But lets check if a server responds to /.well-known/nodeinfo instead.
All other software which supports the diaspora protocol should have this
endpoint by now. Parsing/validating nodeinfo is still handled
gracefully.
closes#8377
* add a class for checking pod connectivity
* extend pod model to handle new functionality
* add an admin frontend to list pods and re-trigger checks manually
* add a daily worker to run through all the pods
* add unit tests for most of the new code