Reorganise the seaweedfs backend in a subpackage
and rename classes for better consistency:
- move WeedFiler in b/seaweedfs/http.py and rename as HttpFiler
- move WeedObjStorage in b/seaweedfs/objstorage.py and rename as SeaweedFilerObjStorage.
Depends on !85 (closed)
Migrated from D6526 (view on Phabricator)