This allow to read settings on the fly even without virtualenv. The ultimate
goal of the commit is to remove utils/brand.env from the git repository.
The code includes a tiny yaml parser that **should** be good enough. The code
read searx/settings.yml directly (and ignore the environment variables).
yq [1] is a more reliable alternative but this require to download a binary from
github which is not great.
[1] https://github.com/mikefarah/yq/#install
