S3 Storage Option for Media files

[yuric]

We are evaluating ADL_LRS deployment on aws/Lambda.

One of the issues we came across was the file storage logic. Since we cannot store files on the OS we are using aws/S3. Is this something you would be interested in future PR for?

Also, what about static file storage on S3? Thoughts on a PR on that?

[ljwolford]

Having it as a separate branch would be great. It would be nice to include an updated README with it, explaining the use of the s3 storage and installation instructions. That could also be a separate wiki page if need be.

[kgrandis]

Hi, I've just created a branch to share work I had done enabling S3 support: https://github.com/kgrandis/ADL_LRS/tree/feature/s3

I haven't made a PR yet as I would prefer others test it further. I don't make much use of the attachment capabilities myself and haven't tested it thoroughly enough.

I've modified the fabfiles a bit to support optional enablement of S3 support. I've updated the readme a bit and provided some preliminary s3-related docs.

This was one of the first steps in dockerizing the project, but thought I would split it out as an independent feature for review.