MongoDB object storage

[ms-xy]

MongoDB can store files, we should have the option to use it as object storage.
Our configuration isn't flexible enough to support this right now, but we could default to MongoDB as object storage if MongoDB is configured as the storage but no object storage is specified.

[webstergd]

Will need to link to issue #15

[cynexit]

@ms-xy I don't see a flexibility issue here, it's as easy as adding a objStorerMongoDB.
That being said, mongo has a lot of pitfalls like the 16mb limit we need to work around which is the reason it's not currently supported as a object storage. However, this is noted for the future.

[webstergd]

We would need to use Mongo's gridfs for storage. Shouldn't be terrible to add.