Handle backlog on startup.

It makes it so that we can restart fedmsg-processes and have them pick
up where they left off... which should be pretty useful for more quickly
debugging and restarting the fmn backend.

This depends on mokshaproject/moksha#17.

This fixes fedora-infra/fedbadges#6.
Update gitignore.
PEP8.
os.path.join.
Merge pull request #266 from fedora-infra/feature/backlog

Handle backlog on startup.