Avoid fbp-diffbot needing admin rights

[jonnor]

The checking and, diffing works fine with just read access.
However configuring the webhooks to automatically follow changes requires admin access.

Need to find a better solution to this...

[jonnor]

Maybe if making this a proper Github OAuth app, then we can ask for permissions to do things on behalf of a user. That could then setup webhooks (once), and also invite the fbp-diffbot user.

[jonnor]

I guess another alternative is to require the admin to manually configure the webhook...