Removes deprecated code.
Renames 'backend' package namespace to 'backends'.
Merge pull request #19 from open-nuage/cleaning

Removes deprecated code and renames backend package to backends.
Moves upload_to method outside Item object for reuse.
Adds hashes to debug fixtures for better testing.
Moves common REST API tests to base TestCase to ensure every backends correctly support it.
Updates API tests by overriding common REST tests and adding only backend features tests.
Fixes bad tests.
Adds common REST tests.
Moves nuage models and tests to the main app.
Moves serializers and viewsets modules to the main nuage.server app.
Removes deprecated backends.localstorage app empty files.
Updates doc.
Small import review.
Moves views to specific module.
Removes unused import.
Moves 'client' and 'qf' tests vars as globals.
Merge pull request #1 from open-nuage/backends-enhancement

No backend for now.
Adds 'Item.hash' field to serialize in readonly.
Adds standard download view.