Add warning if conditional_variance_decomposition is requested with simulated moments
Improve documentation on unconditional variance decomposition
Disentangle computation and display of conditional_variance_decomposition

Previously, noprint suppressed the computation of conditional_variance_decomposition although it should only suppress its display. Also adds a dedicated field for the unconditional variance decomposition.
Merge pull request #646 from JohannesPfeifer/var_decomp

Var decomp