Added mail system

Added mail system.
NOTE: REQUIRES A DATABASE TABLE CALLED `mail` WITH COLUMNS `from`, `to`,
`message` (ALL STRINGS), AND `cleared` WHICH CAN BE EITHER AN ENUM SET
TO 'TRUE' AND 'FALSE' OR A STRING. ALSO NOTE: I WASN'T ABLE TO GET A
CHANCE TO TEST THIS, BUT IT SHOULD IN THEORY WORK.