WIP #50 Create script to poll emails and add to database

Per WIP #50 (https://assemblymade.com/support-foo/wips/50) I have added the following:

* An endpoint for new email to enter the system (Messages::Email.receive)
* A script (bin/mailman) to fetch email from an IMAP Folder. User settings are in .env.example
* A new gem Supportly, created by @Pugio and I to allow for scoped, thread safe sequences. This handles conversation numbers.