Support for fetching WWDC 2010-2013 videos

[zadr]

It would be neat to support all the videos that Apple makes available. I think this is just WWDC 2010-2013 these days.

To do this, I don't think we would need much more than adding a few buttons to the xib in IB (either to the left or bottom of the view?) that have the year on 'em and remain pressed after being clicked. Default to the current year. It would then update _WWDCVideosURL to use the selected year, instead of hardcoding 2014.