Add s3 support

@ckolos I think this is ready to push to staging. I parameterized all input files as URLs. By default the upload to s3 is skipped. If you want we can get rid of the s3_upload flag and just check if s3_url is non-empty.

lists2safebrowsing.py --s3_url <s3://<bucket_name>> --s3_upload

or

lists2safebrowsing.py && aws s3 cp <output_file> <s3://foo>