Db aliases

This PR makes it easy to integrate `notifier` with DBs with different schema names than the ones expected by `notifier`.

For instance, if instead of having your app users under a mongo collection named `user` you would have a hard time integrating `notifier` into it.

You can now specify aliases for collection names easily in your config files:

```js
db: {
  connection: /*...*/,
  aliases: {
     user: "players"
  }
}

...
```

That would make all calls to `db.user` actually use the `players` colleciton in your DB.

The only **change** needed by this PR is that `config` files now have this `db` element and having `connection` inside of it. But the sample file modifications are also included here.

P.S.: I know there are a lot of changes in the PR but that's because I forked *before*  the 0.1.0 release. It shouldn't affect anything.