Optimize all images (shave ~1.2MB off total size)

This change optimizes almost all images in /img in a lossless fashion.
It shaves off 1.2MB on the total size of assets previously being
shipped down the line.
Perf improvement: Switch animated GIF to JPEG

The ~5MB animated GIF we currently ship to all users (including those
on mobile) is starting to cause some pain and should be dropped for a
static header instead.

Reasons:

1. It’s hurting jsconf.eu performance on both mobile and desktop, but
particularly the former. Without the GIF the site scores far better on
webpagetest with almost instant improvements to the speed index.

2. For international users visiting jsconf.eu on their phones and
tablets, they’re going to rack up charges they otherwise shouldn’t just
to check the site and schedule.

3. I love the GIF. GIFs should be everywhere, but only where it makes
sense. The smallest I could get the GIF we use today down to was about
3MB and for <video> instead ~600KB. Contrasting that with a far smaller
sized image of the same resolution, the site would mostly look the same
but just be a little more static.

Would you please consider this? :)
Ensure Compass styles get compressed for prod

The current configuration has preferred output style commented out, so
we’re not actually minifying styles.

Looking at the output on the site, this is confirmed. This will fix it
so that any time we run a `compass compile` the output is minified.
Merge pull request #2 from addyosmani/perf

Some small performance improvements