refactor(editor): the trainset is a tool of its own

The fourth tool out of editor_mode. The track under the cursor and the
first steps of the tutorial become types of their own, which the editor
gives to the tools, and a tool shown as a tab of the lineside panel keeps
its open and expanded flags in a tool_tab. The trainsets waiting for the
save are handed to the editor by the tool, which hears back when they
were written. The self-test command trainset moves with it.

application/editormodevehicle.h

@@ -0,0 +1,79 @@
+/*
+This Source Code Form is subject to the
+terms of the Mozilla Public License, v.
+2.0. If a copy of the MPL was not
+distributed with this file, You can
+obtain one at
+http://mozilla.org/MPL/2.0/.
+*/
+
+#pragma once
+
+#include "application/editortool.h"
+
+#include <memory>
+#include <set>
+#include <string>
+#include <vector>
+
+namespace ui
+{
+class vehicles_bank;
+struct vehicle_desc;
+struct skin_set;
+}
+
+// a trainset put on the selected path, written to the scenery on save, or only to be driven
+class vehicle_tool final : public editor_tool
+{
+  public:
+	explicit vehicle_tool(editor_services &Services) : m_services{Services} {}
+	void draw_overlay() const override;
+	void render_options() override;
+	editor_selftest_result selftest(std::string const &Command, std::istringstream &Words) override;
+	tool_tab &tab() { return m_tab; }
+	void start(TTrack &Track, glm::dvec3 const &Point);
+	bool take_leave();
+	std::size_t trainset_lines(std::vector<std::string> &Lines);
+	void trainsets_written();
+
+  private:
+	editor_services &m_services;
+	tool_tab m_tab;
+	struct vehicle_state
+	{
+		std::shared_ptr<ui::vehicles_bank> bank;
+		char search[64]{};
+		bool controllable_only{true};
+		std::shared_ptr<ui::vehicle_desc> vehicle;
+		std::shared_ptr<ui::skin_set> skin;
+		int driver{0}; // 0: a driver, to be driven; 1: nobody, parked
+		TTrack *track{nullptr};
+		glm::dvec3 point{0.0};
+		std::string placed;
+		std::string status;
+		bool leave{false}; // the editor gives way to the driving at the start of the next frame
+		struct consist_vehicle
+		{
+			std::shared_ptr<ui::vehicle_desc> vehicle;
+			std::shared_ptr<ui::skin_set> skin;
+			bool turned{false};
+		};
+		std::vector<consist_vehicle> consist;
+		int picked{-1}; // vehicle of the train whose buttons are shown
+		std::set<ui::skin_set const *> minis; // skins whose side view was asked for
+		int facing{1};
+		bool write{true};
+		char timetable[64]{"none"};
+		double velocity{0.0};
+		struct trainset
+		{
+			std::string head;
+			std::string track;
+			std::vector<std::string> lines;
+		};
+		std::vector<trainset> trainsets;
+	};
+	vehicle_state m_vehicle;
+	bool place();
+};