Platform update (v2.151)

Payment: add support for refunding PayPal payments
Bookster: balance payments and security deposit management now available on all paid service levels above Solo
- send out emails requesting balance payments
- send out emails requesting security deposit payments
- automatically refund a security deposit
Email marketing: increase the frequency when publishing email addresses to the Email marketing suite
- Send slick, branded emails to enquirers, bookers, managers, website users
- was publishing twice a day, now every 15 minutes

Admin console: add a setting to create damage deposits for manual bookings
Admin console: correctly Audit log Subscription commencement/expiry date changes
Admin console: improve icons used in various places
Booking: fixed bug where the data was not stored when redirecting for some errors
Bookster iCal availability import: add a setting for storing when a feed was last processed, added more debug info to the iCal feeds
RESTful API (beta): updated support for creating a booking