Install aws-sdk
Add AWS initializer and configuration
Generating URLs from saved s3_paths + mime/types
Use uuidv4 for subject filenames

Don't override locations=
Fix failing spec

due to rails silently converting all params to strings in
controller specs. Thanks Rails!
add default aws values for travis test env
Merge pull request #249 from edpaget/s3-subject-uploads

S3 subject uploads