Add tests for various error mail sending scenarios

Add manual transaction handling.

Remove grandfather option

Add in a tracking pixel.

Add in alt text for profile image

Clean up common.

Add the ability to dry-run the command without sending e-mail.

Don't save courses sent during a dry run

Switch to EmailMessage for LinkedIn so we can send HTML emails

Update subject copy.

Use correct name for CertificationName

Fix up certificate url information.

Fix whitelist logic to handle empty lists.

We were using to indicate the date a course ended.  Better to remove it,
since edX certificates don't really expire.

Refactor findusers script to be fully lazy, in hopes we don't run out of memory with huge numbers of users.