Refactor the generation of rules and classes by the PMMLCompiler, for PMML resources containing Tree models.

1. Replace any remaining instances of types declared in rules files with POJOs
2. Reduce and/or remove the usage of rules in the process of generating rules and classes
3. Expose/make available the POJO that is generated from the MiningSchema, so that it can be used as input, instead of PMMLRequestData type
4. Update rules to make direct use of the input POJO