Servers from config

*Not complete, don't merge yet*

This is a start on the work to have Servers configured in config files rather than in the database. I have added Server config to config.groovy in a way that I think will work but feedback on this approach is welcomed. I have updated HostVerifier so that proxy requests use the new Server configuration to validate proxy URLs. There are other usages of Servers which haven't been changed over, yet.
That's also a WMS server, so maybe we should merge it into `wmsServers`?

I would even go with just `servers`, or `allowedServers`. What do you think?