Insufficient Permission errors from Github are poorly propagated to the client

[timperrett]

In the event a user does not have admin privileges on a repo, they cannot enable the webhook Nelson needs. At present the user experience for this is kind of terrible, as we do not handle these 401 responses from Github in such a way that allows us to send an informative message back to users.

Unable to enable project company/name-of-repo. Response was:
{"message":"An internal error occurred"}