R1:e4df9590642d

Use Celerity to version all static resources

Summary:
We don't use versioned URIs for images, so when they change users may get old versions.

This was a particular issue with the recent logo change, which several users reported cache-related issues from.

Instead, use Celerity to manage image URI versions in addition to CSS/JS.

This is complicated, because we need to rewrite image URIs inside of CSS, which means the hash of a CSS file has to be derived from the current image data. Otherwise, when we…