Routes and additional behavior handling private repositories
access -> properties
Merge branch 'private_repositories' of github.com:shin-/docker-registry into private_repositories
Removed exceptions for handling private repos

The code was longer for handling those exceptions. On top of it,
the data raised was not used (which makes the exception raised
completely useless).
Added new line
Re-added comments from Joffrey for private content + fixed typos
Fixed pep8 warning on modules import
Remove cache headers for private content
Removed useless argument
Fixed missing variable
Fixed missing variable
Implemented archive files list on image layers
Hotfix: prevent tarsum compute from crashing with empty layers