pep8 is deprecated, it is replaced by pycodestyle.

The infra to run selenium these tests was too complex, and the test are
not updated since 2016. This patch removes the dependencies of
these tests and it adds `pytest` as runner for the unit tests.

Move spot project to python 3. The support of python 2 is
removed related to the issue https://github.com/asciimoo/searx/issues/1471.

The update is mainly done with `2to3` tool and a lot of changes for
the unicode support (see https://docs.python.org/3/howto/unicode.html)

Close: #7

Below commands to build and run the docker image:

* docker build -t spotenv -f Dockerfile.env .
* docker run -it --rm  -v $(pwd):/ws -w /ws --network host spotenv bash -c "./manage.sh update_dev_packages; ./manage.sh pep8_check; ./manage.sh unit_tests;"

- npm install less@2.7 less-plugin-clean-css grunt-cli is moved inside manage.sh
- if it is possible to source manage.sh to update the PATH (to start grunt)
- tidy the help documentation
- update the geckodriver version to 0.19.1

- prevent whitespace-splitting of variable expansions
- prevent interpretation of values as flags/options

(mostly)

Fix issue #887, #962

./manage.sh don't build css that are built by ./manage.sh grunt_build

Otherwise the script fails with spaces or asterisks in the directory path.