#2131 - Banner subscriptions (eCommerce feature to pay to show your banner)

Also note I don't think current point-store banner sale sets automatic expiration. So when implementing this, we are effectively also pulling the pre-existing feature firmly in the direction of "temporary banners". Or possibly make the existing feature configurable, thus giving the webmaster options for:
1) One-off payment for a permanent banner
2) One-off payment for a temporary banner (how temporary?)
3) Recurring payment for a permanent banner