Ensemble solutions do not store individual solutions

[gkronber]

The ensemble solution is a combination of an ensemble model, an ensemble problem data, and the results.

Later, an item collection of solutions was introduced for visualization of the individual solutions in a view. The individual solutions are however not persisted and instead recreated from the individual models of the ensemble model in the after-deserialization hook. This has the effect that solutions are recalculated when loading ensembles which might take a long time (e.g. for random forests).

Proposed solution: also store the individual solutions of an ensemble solution.

[gkronber]

r12816: added storable attribute to collection of individual solutions and recreate solutions in after-deserialization hook only when the collection is empty.

[mkommend]

Reviewed r12816.

[gkronber]

r13049: merged r12816 from trunk to stable