Add MembershipPayment to hook_civicrm_pre and hook_civicrm_post

This patch will allow module to hook into the the creation of a MembershipPayment using hook_civicrm_pre and hook_civicrm_post. it only works on delete and create. there is no edit operation and I'm not 100% sure the best place to add the view $op, though I'm happy to do it.

We've been using this to allow us to set up a bunch of amortization tables around memberships and to contributions where we need to know an contribution is actually tied to a membership not just that it's labeled "Member Dues"