AliasType plugins

More than happy to move toward that too, my thought was to have the specific plugins first and then unify them. I think that there will be some differences for things like labels, the lowercase label that core now has is an en-specific hack and there's no multilingual label. If we can manage it, more than fine with me.

As for "all the content types", my idea is to have the derivates for entity types with a path field. (+ a separate feature where you can enable the path field for all entity types that don't have it by default, like I'm doing now hardcoded for users)