New implementation

[lazamar]

Replaces legacy implementation with a type-driven approach.
Main points:

• No implicit dependencies relying on runtime checks. Removed use of annotations, everything is checked at compile time now.
• Databases and repositories explicitly initialised.
• Type-safe encoders and decoders for all types.
• Decoders for queries and commands defined locally with route definition.
• Encoders and decoders for Mongo types defined together with the collection.
• Collection instances can define how to create indexes.

[lazamar]

Great work