Create Codec implementation for POJOs

The 3.0.x branch now has pluggable support for BSON codecs (encoders/decoders), as well as a few concrete implementations for Map-like classes: DBObjectCodec, DocumentCodec, and BsonDocumentCodec.

The goal for this issue is to create a ClassModelCodec (and associated ClassModelCodecProvider) that supports encoding and decoding any POJO (Plain Old Java Object).

This codec should support the following field types:

• String
• int, Integer
• long, Long
• boolean, Boolean
• double, Double
• Date
• POJO (for embedded documents)
• Binary
• java.util.List (of any of the preceding types)

It also must provide a way to indicate a mapping for the _id property (by convention or annotation).