GH-1559 Fix FTB icons

This was caused by separation of GUI and logic. Now logic has an interface that GUI implements.
It should be expanded upon later.

application/MultiMC.cpp

@@ -344,6 +344,7 @@ void MultiMC::initIcons()
 	{
 		m_icons->directoryChanged(value.toString());
 	});
+	ENV.registerIconList(m_icons);
 }
 
 

application/dialogs/ExportInstanceDialog.cpp

@@ -346,8 +346,8 @@ void SaveIcon(InstancePtr m_instance)
 		bool saveIcon = false;
 		switch(mmcIcon->type())
 		{
-			case MMCIcon::FileBased:
-			case MMCIcon::Transient:
+			case IconType::FileBased:
+			case IconType::Transient:
 				saveIcon = true;
 			default:
 				break;