Added/removed strengths from StrengthVarManager are not reflected in model

[michi42]

At the moment, adding or removing strengths to or from a StrengthVarManager in a model (using get StrengthVarManager().getStrengthVarSet(). addAllStrengths()) is not reflected in the model: the resulting strengths can be changed, but changes are never passed to MAD-X.

The reason for this behavior is that JMadModelImpl has to register its listener for each strength to be passed to MAD-X. The only happens on initialization but not when the contents of the StrengthVarManager are modified.

To fix this, we would probably have to provide a listener in StrengthVarSet to observe strengths added/removed, and use this in JMadModelImpl to register the listener on the newly added strenghts (or remove it from deleted strengths, respectively).
In a second step, observing and concentrating the changes for all contained strengths could be completely delegated to StrengthVarSet, and the model would only add a single listener to StrengthVarSet (strengthValueChanged(Strength, newValue)) instead of tracking each Strength individually.