Avoid useless impossible import by putting confpsec in a dedicated file

Now it support -v and -f options (kind of dirty support for the moment...)

- now datasources are declared with two conf keys : read_only and identifier
- the old datasources plugin hook is now declared in lodel/plugin/core_hooks.py. This file is imported after lodel/plugin/hooks.py in the loader.py

- defining a new datasource named dummy2 in both tests conf and install/conf.d
- adding two class using the new datasource in em_test.py
 - index : abtract class representing indexes (two fields, name & content)
 - indextheme : thematic index, inheriting from index but with one more field "theme"

They have to implement a _activate() method in their __init__.py file

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

now using examples/em_test.pickle as editorial model for new instances

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

- load variables from settings
- import loader.py

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

Now we have a main page on doxygen