We have a few places in the code where we need to validate various email related settings, and will have another soon with the improved group email settings UI. This PR introduces a class which can validate POP3, IMAP, and SMTP credentials and also provide a friendly error message for issues if they must be presented to an end user.
This PR does not change any existing code to use the new service. I have added a TODO to change POP3 validation and the email test rake task to use the new validator post-release.
