Create model class with a subscribable interface.
function(parentClass, constructor) {
	// inherits methods from parent class
	constructor.prototype = Object.create(parentClass.prototype);
	
	// inherits methods from Subscribable class 
	for(var key in Subscribable.prototype) {
		constructor.prototype[key] = Subscribable.prototype[key];
	}
	
	constructor.prototype.constructor = constructor;
	constructor.prototype._keepHot = true;
	
	return constructor;
}