Integrate mongo into current architecture

@kerwinloukusa This should be the final building block. In order to get things working locally, you'll need to do the following:

* Fire up a local instance of mongodb
* Create a new db (currently called 'climb', but you can call it whatever you want provided you modify the reference in app.js)
* Create a collection called 'workouts'.
* Insert some random workout data into the workouts collection. You can use the stuff that currently resides in stub.json since I edited to be mongo-compatible.