Added a gutter and currentline highlighting to the SQL editor.

Currently gutter only shows linenumbers. Code is mostly from http://doc.qt.io/qt-5/qtwidgets-widgets-codeeditor-example.html

There is a little bit included in this commit from a first try to make toobars adept to the current tab.

Code #2

pglab/CodeEditor.h

@@ -0,0 +1,31 @@
+#ifndef CODEEDITOR_H
+#define CODEEDITOR_H
+
+#include <QPlainTextEdit>
+
+class CodeEditor : public QPlainTextEdit
+{
+	Q_OBJECT
+public:
+	explicit CodeEditor(QWidget *parent = nullptr);
+
+	void gutterAreaPaintEvent(QPaintEvent *event);
+	int gutterAreaWidth();
+
+protected:
+	void resizeEvent(QResizeEvent *event) override;
+
+signals:
+
+public slots:
+
+private slots:
+	void updateGutterAreaWidth(int newBlockCount);
+	void highlightCurrentLine();
+	void updateGutterArea(const QRect &, int);
+
+private:
+	QWidget *gutterArea;
+};
+
+#endif // CODEEDITOR_H