Provide Begin/End events for the whole subwiki creation and intialization

There's two begin/end events currently defined for the subwiki creation: WikiCreatingEvent and WikiCreatedEvent. However those events only framed the creation of the descriptor and the first initialization of the wiki: the WikiCreatedEvent is triggered before the template of the wiki is copied.
It could be useful to have begin/end events framing the whole process of the creation of a wiki, including its complete initialization.