Added the prefixStack optional parameter to the S3 upload task, allowing you to exclude stack from the file path if you prefer.
More library upgrades

In particular RxScala 0.17 => 0.20
UberJar munging
Merge branch 'master' into prefix-stack
Merge pull request #204 from guardian/pw-upgrade-libraries

Upgrade more libraries
Merge pull request #203 from guardian/prefix-stack

Added the prefixStack optional parameter to the S3 upload task
Add custom mime-types for the S3 upload task

We are hosting a firefox plugin on S3 and this must serve with the correct MIME type for firefox
to facilitate installation.