weekly digest implementation
implemented weekly digest emails as a delayed job

* added info about running in README.md
* refactored to be more clear
refactored weekly digest emails as a delayed job
merge with staging
initial setup of weekly mailer with whenever gem
uncommenting comments
delete comments on devise.rb, delete inbound_email.rb, undo feature to delete past old emails as background task
Merge pull request #2 from ohmage/weeklyDigest

Weekly digest with whenever scheduler