Synchronize PlotDock with 'Execute SQL' table. Continuation of PR #1271

Make use of signals to connect the selection in plot to the associated
table widget. Every time that the plot is updated from the Main Window
the table widget associated to the table or query is connected to the plot
and the previous widget is disconnected. This allows the selection of the
correct table widget.

Line selection methods moved to the Extended Table Widget to be used as
slots for this connection.

The destroyed signal is also connected for resetting the plot. This fixes
a crash that already existed before this PR, when closing a SQL tab while
the plot is still associated to the table results model.

src/ExtendedTableWidget.h

@@ -40,6 +40,8 @@ public:
 
 public slots:
     void reloadSettings();
+    void selectTableLine(int lineToSelect);
+    void selectTableLines(int firstLine, int count);
 
 signals:
     void foreignKeyClicked(const sqlb::ObjectIdentifier& table, const QString& column, const QByteArray& value);