Add missing Q_OBJECT macros in header files

Fixes 20 warnings similar to the following ones when generating a translation file with e.g. "make de.ts":
/home/daniel/Lmms/src/tracks/AutomationTrack.cpp:40: Class 'AutomationTrack' lacks Q_OBJECT macro
/home/daniel/Lmms/src/core/FxMixer.cpp:41: Class 'FxRoute' lacks Q_OBJECT macro
/home/daniel/Lmms/src/core/FxMixer.cpp:554: Class 'FxMixer' lacks Q_OBJECT macro
/home/daniel/Lmms/src/gui/widgets/MeterDialog.cpp:52: Class 'MeterDialog' lacks Q_OBJECT macro
...

include/AutomationTrack.h

@@ -32,6 +32,7 @@
 
 class AutomationTrack : public track
 {
+	Q_OBJECT
 public:
 	AutomationTrack( TrackContainer* tc, bool _hidden = false );
 	virtual ~AutomationTrack();

include/InstrumentMidiIOView.h

@@ -38,6 +38,7 @@ class QToolButton;
 
 class InstrumentMidiIOView : public QWidget, public ModelView
 {
+	Q_OBJECT
 public:
 	InstrumentMidiIOView( QWidget* parent );
 	virtual ~InstrumentMidiIOView();

include/MeterDialog.h

@@ -35,6 +35,7 @@ class LcdSpinBox;
 
 class MeterDialog : public QWidget, public ModelView
 {
+	Q_OBJECT
 public:
 	MeterDialog( QWidget * _parent, bool _simple = false );
 	virtual ~MeterDialog();