New extension hooks for register and update_profile

Here are a couple of extra extension hooks that allow a distinction between the end of the register() and update_profile() processes.

As these two processes share the `Freemember_model::update_member()` and `Freemember_model::update_member_custom()` functions there was not an immediate way to know via existing hooks which process was being run.

I'm not sending anything other than `$member_id` to the new hook as I personally didn't need it.