Fix/improve includes/fwd decls

Preparation for clang-format. It will shuffle the includes, and this
preparation will prevent errors from that step.

include/AutomatableModel.h

@@ -34,7 +34,6 @@
 #include "ValueBuffer.h"
 #include "MemoryManager.h"
 #include "ModelVisitor.h"
-#include "ControllerConnection.h"
 
 // simple way to map a property of a view to a model
 #define mapPropertyFromModelPtr(type,getfunc,setfunc,modelname)	\

include/Clipboard.h

@@ -28,6 +28,7 @@
 #include <QtCore/QMap>
 #include <QDomElement>
 
+class QMimeData;
 
 namespace Clipboard
 {

include/ControllerConnection.h

@@ -33,11 +33,11 @@
 #include <QtCore/QObject>
 #include <QtCore/QVector>
 
-#include "AutomatableModel.h"
 #include "Controller.h"
 #include "JournallingObject.h"
 #include "ValueBuffer.h"
 
+class AutomatableModel;
 class ControllerConnection;
 
 typedef QVector<ControllerConnection *> ControllerConnectionVector;

include/LocklessRingBuffer.h

@@ -28,6 +28,7 @@
 #include <QMutex>
 #include <QWaitCondition>
 
+#include "lmms_basics.h"
 #include "../src/3rdparty/ringbuffer/include/ringbuffer/ringbuffer.h"
 
 

include/MemoryHelper.h

@@ -25,6 +25,8 @@
 #ifndef MEMORY_HELPER_H
 #define MEMORY_HELPER_H
 
+#include <cstddef>
+
 /**
  * Helper class to alocate aligned memory and free it.
  */

include/OutputSettings.h

@@ -26,6 +26,7 @@
 #ifndef OUTPUT_SETTINGS_H
 #define OUTPUT_SETTINGS_H
 
+#include "lmms_basics.h"
 
 class OutputSettings
 {