Add OFX plugin support and related infrastructure

This commit extends the OFX plugin support in Olive by:

- Initializing and scanning for OFX plugins
- Updating PluginNode to handle OFX plugin parameters and inputs
- Adding necessary methods and properties for OFX plugin integration
- Enhancing NodeFactory to include OFX plugin nodes
- Refactoring and renaming OliveInstance to OlivePluginInstance
- Introducing new classes for parameter handling (ParamInstance)
- Adding PluginJob for rendering OFX plugins
- Adjusting CMakeLists.txt files to include new source files

app/node/value.h

@@ -163,7 +163,13 @@ public:
      * Resolves to `int` - the index currently selected
      */
 		kCombo,
-
+		/**
+	 * ComboBox type
+	 *
+	 * Resolves to `QString` - the text of choice currently selected
+	 * This is to support the OpenFX type kOfxParamTypeStrChoice
+	 */
+		kStrCombo,
 		/**
      * Video Parameters type
      *