Feature: Pattern import/export (#5891)

* Init

* Suggested changes by @IanCaio, thanks!

* Selecting one file to import is enough.

* Explicit use of TimePos in favour of int where expected, as suggested.

* Make pattern import/export future proof with using DataFile instead of custom code to read/write the pattern file.

* Remove unused/duplicate imports

* Make import/export dialogs file-ext filter consistent.

Co-authored-by: CYBERDEViL <cyberdevil@notabug.org>

include/DataFile.h

@@ -52,6 +52,7 @@ public:
 		ClipboardData,
 		JournalData,
 		EffectSettings,
+		NotePattern,
 		TypeCount
 	} ;
 	typedef Types Type;

include/PianoRoll.h

@@ -47,6 +47,7 @@ class QPixmap;
 class QScrollBar;
 class QString;
 class QMenu;
+class QToolButton;
 
 class ComboBox;
 class NotePlayHandle;
@@ -530,6 +531,8 @@ signals:
 private slots:
 	void updateAfterPatternChange();
 	void ghostPatternSet( bool state );
+	void exportPattern();
+	void importPattern();
 
 private:
 	void patternRenamed();
@@ -539,6 +542,7 @@ private:
 
 	PianoRoll* m_editor;
 
+	QToolButton* m_fileToolsButton;
 	ComboBox * m_zoomingComboBox;
 	ComboBox * m_zoomingYComboBox;
 	ComboBox * m_quantizeComboBox;