Constrain parameters through interfaces

Connecting interfaces could define constraints on to-component parameters given from-component parameters.

• semanticConstraints should always be possible on the supercomponent, provided we can access subcomponent parameters in Functions
• Actual constraints would be ideal to minimize overhead. But these would be constraints between parameters at the same level of hierarchy, not from supercomponent parameter to subcomponent parameter.
• Probably need some form of output parameter then? Or is getParameterValue sufficient? May need a different way of storing constraints (see #13)
• Need to be able to handle loops -- would semanticConstraints still be fine in that case?