DP platform upgraded to v3.5

• Fixed bug where QR code for products didn't always work in all mobile browsers.
• Artist royalty statements now available as PDF instead of CSV.
• Artists can now order complimentary copies of their own work - shop as normal and the shopping cart will make the deductions.
• Several improvements and bug fixes to the core API.
• Numerous administrative features added to make our business operations smarter and more efficient.