Provide a higher resolution AJAX spinner

The previous one was only 32x32 and looked blurry on retina displays,
the new one is 64x64.

This one was generated using only 5 colors and optimized using gifsicle
to keep the size small (2.2KB 64x64 vs. 1.8KB 32x32).

Change-Id: Ie4db93ce819fe8a41fa98b717b2ff5443258b7df
Merge "Provide a higher resolution AJAX spinner"