Enterprise: Add Schema checking

[adamfowleruk]

Sometimes a Schema is necessary. JavaScript is also loosely typed, so is in need of guaranteeing schema moreso than other language bindings.

Two potential Schema features:- JS Schema - enforce data type guarantees in MLDB - prevents database throwing errors on commit DB Schema - load-and-enforce pre-existing schema for pre-listed schema of interest (XML docs only)

Second option will require XML doc support, and Schema admin functions

[adamfowleruk]

Changing milestone as not convinced we need to support this other than error handling.

[adamfowleruk]

Removing this as handled by save() and error handling.