Re-evaluate/refactor KiePMML AST factories

Re-evaluate implementation of KiePMML AST factories in the view of the mining model specifications.

Reevaluate usage of fieldTypeMap - types.

E.g.: inside 

DroolsModelProvider.getKiePMMLDroolsASTCommon the 

Map<String, KiePMMLOriginalTypeGeneratedType> fieldTypeMap is populated invoking 

addTransformationsDerivedFields. Then, a  List<KiePMMLDroolsType> is created out of this map.

Later the same map is also populated by 

KiePMMLDataDictionaryASTFactory.factory(fieldTypeMap).declareTypes(dataDictionary).

and the List<KiePMMLDroolsType> retrieved by the latter are added to the one created before.

That means it is not needed to have KiePMMLDerivedFieldASTFactory and KiePMMLDataDictionaryASTFactory returning List<KiePMMLDroolsType> - they can simply instantiate and return a Map<String, KiePMMLOriginalTypeGeneratedType>; the maps may be merged together, and the List<KiePMMLDroolsType> may be created out of that (merged) map.

So

1) KiePMMLDataDictionaryASTFactory and KiePMMLDerivedFieldASTFactory should return only a newly instantiated Map<String, KiePMMLOriginalTypeGeneratedType>

2) inside DroolsModelProvider.getKiePMMLDroolsASTCommon those maps should be merged 

3) List<KiePMMLDroolsType> should be created out of the merged map 

4) merged map and  List<KiePMMLDroolsType> should be propagated as parameters