Data dumps

Fixes theodi/shared#55

Not quite ready for merge, but this PR adds a couple of Rake tasks to download all data for certificates, one that gets all data (which I imagine will only be run once), and one that gets the certificates which have been added since the last update was done. The dump file is then uploaded to our Rackspace cloud files instance.

Still needs tests, though these may be a bit tricky to do, especially as Fog doesn't (yet) have mocking for Rackspace cloud files.