Properly deal with tweetWorker errors from the Twitter API

[crcastle]

If the worker encounters an error posting a scheduled tweet to Twitter, it will fail silently. The user won't be given any indication of this error. This error should be surfaced to the user somehow so he can fix the problem.

Most of the work for this will be on the AWS Lambda function repo paired with this repo. Keeping the work item in this repo for simplicity.