PrintrBot Blower Fan Mount

[Studies have shown](http://www.desiquintans.com/coolingtests2) that a lot of air in a little spot is good for your 3d prints! I figure a blower fan will really jam some air in there, so why not give it a try?

This is *sort of* a remix, given that I made a new file from scratch, which was inspired by the original! I had a smaller blower fan (27mm x 20mm opening OD) that I'd scavenged from an old projector (they have so many fans in there!), so I needed a model with different opening dimension