Fixed slideshow preset sizes.  #1557

Since _os_slideshow_region_size() defines the preferred sizes for slideshows in different regions I went back and adjusted the sizes for my image styles.  Instead of using arbitrary values, I use the ones the slideshow will try to use.  This currently equates to 980 (max full width), 680 (content area with one side bar), 480 (content area with two side bars), and 300 (max sidebar width).  Footer sides are a little different and a sidebar in the presence of another side bar will only be 250, but those are reasonable amounts for browser scaling.  And the slideshow isn't meant for those regions anyway.
Merge branch 'SCHOLAR-3.x' of github.com:openscholar/openscholar into SCHOLAR-3.x