Servers from config

*Ready for someone to take over - feel free to contact me for any questions*

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.
I don't think HostVerifier is going anywhere soon though. Besides, it has pretty simple logic and probably 100% test coverage.