- creating a function in webui/main.py root_url() that returns the root url without trailing /
- use this function in router and template/loader

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

To start in standalone uwsgi set lodel2.webui.standalone=True in conf file and start loader.py

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