Ran images through ImageOptim.

This saves around 50KB of total file size with no observable degradation.
Merge pull request #2725 from refinery/optimise-images-with-imageoptim

Ran images through ImageOptim.
Merge pull request #1 from refinery/master

Update to refinery/master latest
Add shared example 'an image uploader'
Add 'uploader' tests to images_spec
Merge pull request #2726 from anitagraham/ImageSpecPart2

Shared example 'an image uploader'