CRM-13261 new apiwrapper hook

As discussed on the a-team list. @totten was participating, might be better he validates this PR.

Documentation question: where should I document the new hook? I'm a bit lost in the namespaces in the wiki.

As for an example, is this enough to point to the bounce as activity extension (still have to push the latest version)?

https://github.com/TechToThePeople/betterbounce/blob/master/betterbounce.php#L9