Our old spinner.gif is one of the ugliest remaining parts of Review Board. It's

not retina-aware, and it feels pretty out of place in the modern world.
This change swaps out most of the uses of spinner.gif to use Font Awesome's

fa-spinner icon. This uses CSS transforms to rotate the image, and scales

cleanly to any size and resolution.
There are a couple more uses of the old spinner (in rich text rendering and the

new review request/upload diff UIs) which I have yet to clean up. I'll get to

those in a later change.

Looked at each piece of UI (often by making manual changes to the code to

ensure that the spinner stayed on screen long enough to really verify it).