Log management improvement

This Pull Request is for inform you and launching tests with Travis step by step as I make changes.

For now:
 * Change Event\Event namespace to just Event
 * Adding section on logs in doc
 * Plugin can define custom log action (see documention for more information)

While developping this enhancement I keep the blog plugin up-to-date in order to have at least one plugin with all enhancement for example.

Of course they will be some backward compatibility issue with plugin as some namespace change and some translation text can be missing, no big deal in fact.