Minor changes and refactoring for psi_pred and psi_truth

Minor changes and refactoring in:
    * structured output machines
    * structured output models
    * CResults structure
to remove result->psi_pred and result->psi_truth
@tklein23 This thing does not break the PrimalMosek solver. Yes, it introduces performance penalty as we have to compute join_feature_vector twice for each iteration.