Display random selection & sorting of listings

[gamebits]

For the Curated Lists block, Noozhawk has requested these two features, which could be useful for classifieds or other sold listings:

1. Make it possible to display a random group of listings. Noozhawk often "promos" a set of listings by showing 2–3 on a page, and on their current site they set this to be random so that every listing has the potential to appear and no one listing gets more screen time/exposure.
2. Make it possible to sort the listings in random order. Similar to above, sorting listings in random order ensures any listing has the potential to be at the top of the page, regardless of its alphabetical or publication date order.

[jbwhong]

+1 for this.