MongoOptions Support fixes #36

I've implemented, in a separate Object, the loading of custom mongo options from a config node under mongo source in application.config. I really needed to increase the number of connections per host as I'm using the plugging in a web app with a high throughput  and it was throwing a lot of "Out of semaphores to get db connection" exceptions all the time.
In the plugin I create a MongoConnection with MongoOptions only if some is present in the configuration.
I've also created the proper tests for all the code I've added.

Thank you for creating such a nice and useful plugin!

Gaston M. Tonietti
@ktonga