(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.
FINE! Let's just have a hack day solely dedicated to making the packaging repo better. Like, pair programming, but with the whole team. And probably not working on one PR, but everyone submitting their own, and everyone reviewing them, all focusing on refactoring and improving the packaging repo. Yes?