Allow hub calendars to sell calendar products:
When a user uses "submit event" to submit their event to a hub, the hub will have the option to define and sell products for actions like:
- submitter to pay to submit his event to the calendar
- submitter to pay for his event to be manually made featured event by the hub owner
- submitter to pay for his event to be added to a certain category or tag by the hub owner
- submitter to pay for his event to be promoted by email to hub's visitors by the hub owner
All the above are examples of MANUAL promoting actions that the calendar owner can charge submitter for.