- 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...

Methods are written.
They are not called by anyone and the only tests that were done is that no syntax error is raised.
( refs #131 )

- now plugin is able to instanciate using the good child class
- the discover cache now contains plugin's type

- now we have a LodelHook to trigger migration handlers loading
- datasources initialization in dyncode is now trigger by a hook (lodel2_plugin_loaded)
- datasources loading by dyncode is better