Share internal copy-paste buffer between different table views

Use a shared internal copy-paste buffer for all table views in the
application instead of having one buffer per view. This is not only less
confusing because it more closely resembles the behaviour of the system
clipboard but it also allows copying BLOB data from a Execute SQL result
view to a Browse Data table.

src/ExtendedTableWidget.cpp

@@ -15,6 +15,8 @@
 #include <QBuffer>
 #include <QMenu>
 
+QList<QByteArrayList> ExtendedTableWidget::m_buffer;
+
 namespace
 {
 

src/ExtendedTableWidget.h

@@ -39,7 +39,7 @@ private:
     void useAsFilter();
 
     typedef QList<QByteArray> QByteArrayList;
-    QList<QByteArrayList> m_buffer;                 // TODO: Shouldn't this be static?
+    static QList<QByteArrayList> m_buffer;
 
 private slots:
     void vscrollbarChanged(int value);