Add support for replicaSet mongo setups by passing in an array of server parameters in the form of [<hostname>, <port>, <options>]

eg.
[
	['db1.domain.com', 27017, { auto_reconnect: true, slave_ok: true }
	['db2.domain.com', 27017, { auto_reconnect: true, slave_ok: true }
	...
]
comment endpoint
break out database config into separate files

 - shared 'database.js' for tests and server
 - minimizing use of `throw` in anticipation of bigger refactor

Aside: I'd like to move to more node.js idiomatic callback(err,thing)
wherever possible in Cube, probably as a major semver release.
merge #27 from @LemonCake
allow mongo connection string URLs in config
0.2.8