feat: Implement OFX plugin support infrastructure

This commit adds comprehensive support for OFX plugins in Olive, including:

- Add plugin node infrastructure with getPlugin() method
- Implement OliveHost for managing OFX plugin instances
- Create OliveInstance to handle plugin parameter and timeline interactions
- Add OliveClip implementation for plugin clip handling
- Implement region of definition (RoD) and region of interest (RoI) functionality
- Add interactive mode support in Current class
- Integrate plugin rendering into RenderProcessor
- Fix include dependencies and remove unused OlivePlugin.cpp reference

app/node/node.h

@@ -1124,7 +1124,12 @@ public:
 
 	static const QString kEnabledInput;
 
+	std::shared_ptr<OFX::Host::ImageEffect::ImageEffectPlugin> getPlugin();
 protected:
+
+	// If is set, this is a plugin node.
+	std::shared_ptr<OFX::Host::ImageEffect::ImageEffectPlugin> plugin;
+
 	void InsertInput(const QString &id, NodeValue::Type type,
 					 const QVariant &default_value, InputFlags flags,
 					 int index);