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.
Because of the way the Grails config loads I couldn't see a way (without duplicating the whole thing) to get baselayerServer into the list of knownHosts. Whoever picks this up is welcome to try.