filter: add filter preset undo commands

Add undo commands to add / edit / delete filter presets.
These are styled after the other undo commands: On changes,
the UI is informed by DiveListNotifier signals. Editing is
a simple std::swap of values.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

commands/command_filter.h

@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0
+// Note: this header file is used by the undo-machinery and should not be included elsewhere.
+
+#ifndef COMMAND_FILTER_H
+#define COMMAND_FILTER_H
+
+#include "command_base.h"
+#include "core/divefilter.h"
+
+struct FilterData;
+
+// We put everything in a namespace, so that we can shorten names without polluting the global namespace
+namespace Command {
+
+class CreateFilterPreset final : public Base {
+public:
+	CreateFilterPreset(const QString &name, const FilterData &data);
+private:
+	// for redo
+	QString name;
+	FilterData data;
+
+	// for undo
+	int index;
+
+	void undo() override;
+	void redo() override;
+	bool workToBeDone() override;
+};
+
+class RemoveFilterPreset final : public Base {
+public:
+	RemoveFilterPreset(int index);
+private:
+	// for undo
+	QString name;
+	FilterData data;
+
+	// for redo
+	int index;
+
+	void undo() override;
+	void redo() override;
+	bool workToBeDone() override;
+};
+
+class EditFilterPreset final : public Base {
+public:
+	EditFilterPreset(int index, const FilterData &data);
+private:
+	// for redo and undo
+	int index;
+	FilterData data;
+
+	void undo() override;
+	void redo() override;
+	bool workToBeDone() override;
+};
+
+} // namespace Command
+#endif