Proposed setup for sigul bridge/server for review

[Jesse Keating]

Here is my initial stab at a class for the signing server(s).

There is a bridge that clients communicate with (and I'm thinking
of forcing this through an ssh tunnel through bastion) and that
interacts with koji.  There is also the server itself that has
the gpg keys on it and does the signing action.  The server
initiates a connection to the bridge, so only the bridge has to
listen for connections.

I think I have this mostly setup right, but I'd like some more eyes
on it before I commit.  Thanks!

--
Jes