Optimize images

This branch optimizes all images in our repository by running [image_optim](https://github.com/toy/image_optim) from an EC2 Ubuntu instance using the following command from the root directory of the repo:
`image_optim --pngquant-quality 65-80 -r .`

Overall, the optimizations reduce filesize by 47.81% or 132.7MB across all of our images.

This should drastically reduce the download size across our whole website with little (undetectable) quality loss.
However, since it's a global change we should manually look over the transformed images to make sure everything is as it should be. Also, if there's any images in particular that need to remain untouched, we should revert to their original version.