Add optional delete from disk in collection and playlist

Fixes #284

src/dialogs/deleteconfirmationdialog.h

@@ -0,0 +1,43 @@
+/*
+ * Strawberry Music Player
+ * Copyright 2020, Jonas Kvinge <jonas@jkvinge.net>
+ *
+ * Strawberry is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Strawberry is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Strawberry.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef DELETECONFIRMATIONDIALOG_H
+#define DELETECONFIRMATIONDIALOG_H
+
+#include <QDialog>
+#include <QDialogButtonBox>
+#include <QStringList>
+
+class DeleteConfirmationDialog : public QDialog {
+  Q_OBJECT
+
+ public:
+  DeleteConfirmationDialog(const QStringList &files, QWidget *parent = nullptr);
+
+  static QDialogButtonBox::StandardButton warning(const QStringList &files, QWidget *parent = nullptr);
+
+ private slots:
+  void ButtonClicked(QAbstractButton *button);
+
+ private:
+  QDialogButtonBox *button_box_;
+
+};
+
+#endif  // DELETECONFIRMATIONDIALOG_H