Setup Rollbar as external exception handler

Added 'rollbar' gem to Gemfile, and generated initializer for Rollbar.

Initializer configured to use 'current_author' to access the current
user. Furthermore configured to use async submission to rollbar.com via
sidekiq ('rollbar_messages' queue).
Sending info msg to rollbar when Backup done

Whenever the backup sidekiq job is done successfully, we are sending a
message with level == info to our Rollbar account.
updated gitignore
Don't store development info in repo