typo
added dotenv-rails gem for development convenience.
added SubmissionZipper rescue worker.

- `SubmissionZipper` is a resque worker that zip all the submissions of the challenge and notify the zip file to the requestor
- `SubmissionZipperMailer` is also added to handle notification email of SubmissionZipper
- `rubyzip` gem is added
- added Rake tasks
bug fix : when the zip file exists in S3, notification email does not include the link of zip file.
Merge branch 'cs-2516-zip-s3-files' of https://github.com/aproxacs/cs-website-cms into aproxacs-cs-2516-zip-s3-files
tweaks for submission zipper