Parse rotation field on metadata
Consolidating processing into single job

This should help reduce problems likely caused by constantly fetching the photos
from AWS, as well as enabling support for affecting the images based on the
metadata, i.e. rotation.
Cache S3 data fetches in memcached to reduce generation time

This implements our own wrapper around the Dragonfly S3 store, caching
retrieval for 5 minutes (currently) so that processing multiple image
sizes doesn't require multiple fetches.
Merge pull request #146 from robotmay/auto-rotate

Improvements to image processing.