ExtendedTableWidget: Always scroll per pixel horizonzally

Always use per pixel scrolling when scrolling in horizontal direction.
This changes the scrolling in the SqlExecutionArea and makes some
settings in the MainWindow dispensable.

src/ExtendedTableWidget.cpp

@@ -10,6 +10,8 @@
 ExtendedTableWidget::ExtendedTableWidget(QWidget* parent) :
     QTableView(parent)
 {
+    setHorizontalScrollMode(ExtendedTableWidget::ScrollPerPixel);
+
     connect(verticalScrollBar(), SIGNAL(valueChanged(int)), this, SLOT(vscrollbarChanged(int)));
 }