Added an AbstractDialog class and using it as base for a NewItemDialog class (no new item functionality yet).

Dialogs/abstractdialog.h

@@ -0,0 +1,33 @@
+#ifndef ABSTRACTDIALOG_H
+#define ABSTRACTDIALOG_H
+
+#include <QDialog>
+
+class QGridLayout;
+class QDialogButtonBox;
+class QVBoxLayout;
+
+class AbstractDialog : public QDialog {
+  Q_OBJECT
+ public:
+  AbstractDialog(QWidget* parent = nullptr);
+  virtual void createContent() = 0;
+
+  /// QDialog interface
+ public slots:
+  void show();
+  void accept() override;
+  void reject() override;
+
+ protected:
+  void centerInParent();
+
+ protected:
+  QWidget* m_contentContainer;
+  QVBoxLayout* m_outerLayout;
+  QDialogButtonBox* m_buttonBox = nullptr;
+
+  void closeEvent(QCloseEvent* event) override;
+};
+
+#endif  // ABSTRACTDIALOG_H