(CPR-52) Add support for the automatic building of nightly signed repos

This PR defines a small stack of rake tasks that handle the signing and shipping of repos for a nightly repo. In the process several rake tasks were moved into the appropriate libraries and some additional utilities were added. This PR also deprecates the gpg_name config setting in favor of the gpg_key, and adds a new signing_server config setting for use in automatic signing.
Ah, right, mostly I was wondering where create_repos was used, but I missed it. I'm satisfied with this explanation. Thanks!