Labels

Here is the new behavior regarding the _Need more reviewers_ error message.

* `in_work` if "WIP" is in the title
* `in_review` if a "needs more reviewers" error is found
* `in_integration` if no "needs more reviewers" errors are found

**NB** It won't create those labels for you.

Other changes:

* messages errors are using the same format than PEP8 error messages with codes and consistent line numbering.
* _signature is missing_ triggers _needs more reviewers_ as well.