GitLab

It raises potential error of the response. It is useful to inform
the user of a potential error.

```
dh_clean: Compatibility levels before 9 are deprecated (level 7 in use)
```

https://www.debian.org/doc/manuals/maint-guide/dother.fr.html#compat

- Debian 7 "wheezy" was launched in 2013. Its regular support
  ended in 2016. Its long term support ended in 2018.
- Ubuntu 14.04 "Trusty Tahr" was launched in 2014. Its regular
  support ended in 2019. Its long term support will end in 2022,
  but we already don't use it any more and old versions remain.

- This library is not actively developed, so let's remove old
  stuff to ease maintenance and improvements.
- Old versions can still be used.

Closes #2 (of Heptapod on forge.extranet.logilab.fr)
#2

- It is helpful not to have to write RQL request.
- It is useful for a private project and may be useful to others,
  so there every one will can enjoy it.
- There is currently no automatic test, but it is planned to add
  some in a future patch. As it only adds things, it breaks
  nothing, so we can give new features and test later, even if
  it is bad. But it has the advantage to review less things in
  one time.

Closes #3 (of Heptapod on forge.extranet.logilab.fr)
#3

- It is helpful not to have to write RQL request.
- It is useful for a private project and may be useful to others,
  so there every one will can enjoy it.

- It is helpful not to have to write RQL request.
- It is an improved version of code already in production for a
  private project.

- It is helpful not to have to write RQL request.
- It is an improved version of code already in production for a
  private project.

- Use a new test case class (as the old one was removed from CW)
- Execute GitLab CI only in Python 3 as Python 2 support was
  already removed in tox
- Add missing requirements for testing
- Define a specific Python version, because logilab-common is
  currently broken with Python 3.8 and above, because `cgi.escape`
  has been removed.

Python 2 is not maintained anymore.
https://www.python.org/doc/sunset-python-2/

The former function got dropped in changeset 793a8b8450b1 but client
code in cwcompleter.py did not get updated.