Move code to a deployment engine

TODO: Lots of work remains to move constants off site to the
engine, update tests, reduce dependencies between the engine and
the site - but the code is now separated.
Make the Site __init__ API more consistent
Move S3 settings to the S3 class
Refactor setup. Move packages around a bit.
Break down File in multiple objects
Remove setting site on file objects
Extract file and deployment shared code to bases
Refactor S3 tests
Add support for GCS
Credentials Manager is now a part of DEngine
Make the provider election cleaner
Fix multithreading bug in GCE engine
Added support for Rackspace Cloud Files
Reuse the workflow for all deployment engines

Note: This massively breaks AWS integration tests -- those need to be
fixed
Add a few TODOS...
Update tests a bit (they still fail)
Add this to the list of work remaining!
Add tests for the base Deployment Engine
Update S3 integration tests
Update CredentialsManager tests