In MergeView, replace QTableWidget with QTableView with custom model (#266,#217)

QTableWidget was a major bottleneck for large merge sources (#217).  This is because a QTableWidgetItem needed to be created for every field in every record of the merge data, whether they are being displayed or not.  This was not a problem for small merge sources (only a few dozen records max), however for larger data sets this would severely affect performance and make the application unresponsive.  QTableView only renders the fields and records currently visible.

glabels/MergeView.h

@@ -64,22 +64,18 @@ namespace glabels
 	private slots:
 		void onMergeChanged();
 		void onMergeSourceChanged();
-		void onMergeSelectionChanged();
 
 		void onFormatComboActivated();
 		void onLocationBrowseButtonClicked();
 		void onSelectAllButtonClicked();
 		void onUnselectAllButtonClicked();
 		void onReloadButtonClicked();
-		void onCellChanged( int iRow, int iCol );
 
 
 		/////////////////////////////////
 		// Private methods
 		/////////////////////////////////
 	private:
-		void loadHeaders( merge::Merge* merge );
-		void loadTable( merge::Merge* merge );
 		static QString printableTextForView( QString text );
 
 
@@ -97,7 +93,6 @@ namespace glabels
 
 		QString mCwd;
 
-		bool mBlock;
 		int  mOldFormatComboIndex;
 
 	};