Move events from inner classes to their own package

[palra]

We should stop put events in inner classes, for more readability. Also, it is more easier for a future developer to find the events classes in a dedicated package than searching on a class. Inner classes should be used if we really need to access inner attributes of the parent class, but that's not the case, as we pass them in argument.

My proposal is to create a package event in our working package (for example : fr.univdevs.mmorpg.engine.event) and put subpackages for each topic (fr.univdevs.mmorpg.engine.event.action)