There were manual import through importlib, we have to replace them with LodelContext calls.
Actually the plugins module is in a dirty state....

- 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...

- webui fix in cookies handling
- ram_session fix in token generation (return an str : hex representation of os.urandom(n))
- more fixes in Client session handling

Created a new class LodelSession to handle session datas
Created an automatic wrapper to acces to session handler plugin function throug SessionHandlerPlugin class methods
Bugfixes done for plugins. The plugin type is store in __plugin_type___ and not in __type__