WIP: Migrate content from Azure Blob Storage to Rackspace CloudFiles

Added two work in progress scripts:

1. Generate a list of URLs (DZI + tiles) from a Zoom.it ID: `./scripts/content-urls._coffee <ID>`
2. Migrate list of URLs from Azure to Rackspace CloudFiles: `./scripts/migrate-content._coffee <file>`

Major issue I ran into is that tiles didn’t have proper `content-length` despite setting the headers using `pkgcloud`.

/cc @kenperkins @aseemk