(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.
Yea, so I walked down this road again, and we have too much coupling between rake and the library for this to be feasible today. We'll need to do some work on adding the fetch/load extras into the library, or moving it out somewhere else like a data service before this will work.