Update external libraries.
Resize user images; add a UIImage category.

The maximum size of Wired user icons has increased in the latest
Mac version, from 32px to 64px, so that they'll be retina ready. If
we don't resize all the icons to 32px then they'll start overflowing
the cells.
Revert back to square user icons.
Swap from Git submodules to CocoaPods.