The class PropertyConditionController models the PropertyCondition.
It serves as a superclass for ConditionControllers that want to offer the comparison
of a property against a value.
It presents the user with an operator combo-box. Anything beyond that element is
provided by the subclasses. Subclasses can also choose not to include the operator
combo at all (as in
SetCurrentTimeAction ), although this is rare.
author: Sebastian Nozzi.