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/pluginSupport/OliveHost.h

@@ -15,6 +15,8 @@
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
+#ifndef OLIVE_HOST_H
+#define OLIVE_HOST_H
 #include  "ofxhHost.h"
 #include "ofxhImageEffectAPI.h"
 #include "ofxCore.h"
@@ -66,4 +68,5 @@ private:
 	QList<OFX::Host::ImageEffect::Instance*> instances_;
 };
 }
-}
+}
+#endif