interface for model storage
+method for getting available revision IDs
first test
get rid of parameters in test method
test for model serialization to contain necessary prefixes
restore() should return model serialization, not the model itself.
 The other way round storage implementation would be specific to model implementation, which is obviously a bad design
rename Model to Classifier to prevent mixing up entities (Classifier is a part of PredictionModel)
add method to restore model from serialization
store model state by revision ID, not RevisionInfo object
+model storage impl stub
+more tests
fix test compilation
make PredictionModel an interface instead of an abstract class
test for restoring model from serialized state
add missing test annotation
add method for classifier state serialization (for further implementation using Weka serialization tools)
minor
model index provider /adapter between model and storage/
memory impl for storage to test design
mock implementations for entities in tests