MongoFile 3.0.x implementation

This is a MongoFile implementation that is a complete replacement for GridFS ( but 100% compatible if compression is disabled ) that falls very much in line with the changes in the 3.0.x code base. 

It also includes an optional re-factoring of the GridFS implementation if that code needs to move forward.

After completing the migration of the code from my library, the code separation between the driver and driver-compat projects changes things a bit. I had to split the classes that both implementations shared, so the MongoFile implementation is independent of the GridFS implementation. Thus the GridFS implementation could be deprecated and faded into the electronic sunset.

The central service object in the MongoFile implementation is the MongoFileStore where the read/write operations all start from.

Start by checking out the org.mongodb.file.MongoFileStoreTest.java JUnit test to see a basic usage example.