Fix instrument window tab sizes

- Fix the instrument window tabs minimum width and height formulae
- Also set minimum height and width for instrument tab

include/InstrumentTrack.h

@@ -427,6 +427,9 @@ protected slots:
 private:
 	virtual void modelChanged();
 	void viewInstrumentInDirection(int d);
+	//! adjust size of any child widget of the main tab
+	//! required to keep the old look when using a variable sized tab widget
+	void adjustTabSize(QWidget *w);
 
 	InstrumentTrack * m_track;
 	InstrumentTrackView * m_itv;