[FEATURE REQUEST] Social Media exportable collections

[BrightRaven]

Our content is shared on social media a lot, especially facbook. It would make sharing pins easier when people want to list their "traders" or "wants" if we could create a way to do this.

I suggest making it possible to export an entire collection to a single image compilation (one file, with labels) and a text version where it lists each pin by name and each name is a link back to the relevant pinster image.

This would ideally be available as some kind of dropdown from a button for social media sharing within a collection as a whole (not on individual pins).

[scytherswings]

Requires #81