Update the thor task that builds the webapp archive

This will build a tar file needed by the webapp, lab-interactive-management, and store it on S3. The tar file will have the current HEAD commit's short hash in it's name as well as the URL where it can be accessed on S3. 

thor build_server_achive:upload_tarball

# Will create https://lab-staging.s3.amazonaws.com/lab_1c4d315.tar.gz

This will build the tar file from the contents of the public directory.