+ Registry: Add the new registry support

Handled wrong user credentials by re-init the auth file (it was impossible to login after having wrong crendentials)

Fixed checksum computing. Ensure checksum is computed when image metadata is loaded from disk. Fixed docker push workflow. Moved hash computing to utils

Changed some of the routes to reflect changes made to the API ; added HTTPClient singleton to the graph object

Reimplemented feature: downloading all tags on a repository using docker pull. Temporarily commented out CmdPush

Implemented new version of PullRepository. Missing support for whole repository pull (= no tag specified)

added Docker Index search API doc

added new sphinx contrib extention for better REST API docs, and changed the index search API so that it uses the new docs, as a test to make sure it works correctly