Move slotValueChanged method from base to subclasses because it needs special handling
Add a special case for EffectManifestParameter::VALUE_ENUMERATION
Make getOptions() method const because it is being called on a const object
Set the number of states for each EffectButtonParameterSlot
Add special treatment for EffectManifestParameter::VALUE_ENUMERATION (wrap around the values)
Add button parameters to EffectManifest; also consider the case when min and max are not defined by plugin's manifest
Handle button and enumeration parameters (currently crashes when changing the effects)