Pytest-invenio

- Remove pytest-celery because it's still an alpha release.

- BACKWARD INCOMPATIBLE: Changes to use isort, pycodestyle and pydocstyle via
pytest plugins. You need to update `pytest.ini` and remove the ``--pep8``
from the addopts and instead add ``--isort --pydocstyle --pycodestyle``:

.. code-block:: ini

addopts = --isort --pydocstyle --pycodestyle ...

In `./run-tests.sh` script you should also remove calls to pydocstyle and
isort as both are now integrated with pytest.

- BACKWARD INCOMPATIBLE: Upgrade dependencies: coverage, pytest-flask,
check-manifest, pytest. You need to set the pytest-flask live server
fixture scope in your pytest config:

.. code-block:: ini

[pytest]
live_server_scope = function

- Decommission pytest-pep8 (last release in 2014) in favour of pycodestyle.

- Add `entrypoints` fixture to allow injecting extra entry points during
testing so that you avoid manual registration of e.g. mappings and schemas.

- Add `docker-services-cli` as dependency to enable Invenio modules to
perform reproducible tests.

- Move check-manifest, coverage, isort, pydocstyle, pytest-flask and
pytest-pep8 from test to install requirements to provide them as centrally
managed dependencies.

- Uninstalls numpy in Travis due to incompatibilities with
elasticsearch-py.