Support Multiple Databases

[MrXyfir]

• Move server/lib/mysql-wrap to its own package admyn-database-mysql OR simply keep it and other future database interfaces somewhere within server/lib OR have built-in interfaces but support external ones as well.
• Allow the user to pass a database interface to the admyn Express middleware.
• Initially just require connect(), query(), and close() methods.
• Eventually add methods for each controller (getDatabases(), getTables(db), etc) to allow databases with which the current hard-coded SQL will not work.