Added isValid_ boolean to AMCurrentAmplifierCompositeView, used to indicate whether both amplifiers are valid.
Commented out duplicate slots onSR570ViewChanged(AMCurrentAmplifierView::ViewMode) in IDEASScalerView, REIXSScalerView, VESPERSScalerView.
Added new pure virtual methods to AMCurrentAmplifierView: onMinusClickedImplementation(), onPlusClickedImplementation(), refreshViewImplementation(), and isValid(). Implemented these methods in AMCurrentAmplifierSingleView and AMCurrentAmplifierCompositeView."