Basic email structure plus distributed locking system
Added metadata to mail sent schema
Updated sendwithus to fix memory leak
Updated locking/release procedure
Changed name of mail sent collection
Some emails working
Progress on employer new candidates available email
Employer candidates available email completed
Async must not break upon sendwithus failure
Made mail system resilient to redis failures
Reviewed code, almost ready for release
Hard code mail tasks and add unsubscribe
Fixed misc bugs
Encode/decode emails as URIs

This helps to handle special characters like plusses.
Initialize value of this.redisNotAvailable
Remove testing conditions
Removed mail task from server mapping
Removed old comment
Merge pull request #1342 from codecombat/feature/mail-system

Feature/mail system