- updated scripts etc
- make tests pass

Theorically all of those imports were tested by unit testing, but we've got no inssurance about that.
And even if unit tests had check for syntax errors, all pieces of code were not tested. We cannot
be sure that an import was missed or forgotten...

broken nginx conf + absolute path in slim that is known only at build time

using --plugin option instead of uwsgi_python3 shortcut (can be uwsgi_python34 etc)

Adds a LODEL2LOGDIR to buildconf.py
Adds a nginx-conf option to slim
...

Using execl instead of fork to preserv the pid

SLIM is now able to edit configuration from CLI, to start instances etc.

Avoid useless impossible import by putting confpsec in a dedicated file

- renamed Plugins class to Plugin
- an instance represent a loaded plugin
- classmethod allows to preload & load plugins

- create_instance.sh create some symbolic links
- webui plugin that add webui configuration variable