GitLab

Add back six dependency and change pbtxt files to reflect new way of using own data to train object recognition models

Correct documentation so all commands should be run from the root
of the git directory.

Also clarifies usage on label maps. In a nutshell, label map IDs
should start at index 1 (and not include 0).

* Change dictionnaries iteritems() to items()

Also use the url link to github because *.md files are not
rendered when using jupyter notebook

1 should not shuffle during evaluation; 2 num_readers should be one, or each sample would be evaluate for (num_reader) times and only (num_examples / num_reader) distinct samples are evaluted.