Add recursive sub-folder image browsing

Add toggle button in the top toolbar of the file browser to activate or
deactivate recursive browsing. Toggle state is saved in options.

Limit recursion depth and explored directory count.

rtgui/filecatalog.h

@@ -54,6 +54,13 @@ public:
     typedef sigc::slot<void, const Glib::ustring&> DirSelectionSlot;
 
 private:
+    struct FileMonitorInfo {
+        FileMonitorInfo(const Glib::RefPtr<Gio::FileMonitor> &file_monitor, const Glib::ustring &file_path) :
+            fileMonitor(file_monitor), filePath(file_path) {}
+        Glib::RefPtr<Gio::FileMonitor> fileMonitor;
+        Glib::ustring filePath;
+    };
+
     FilePanel* filepanel;
     Gtk::Box* hBox;
     Glib::ustring selectedDirectory;
@@ -95,6 +102,7 @@ private:
     Gtk::ToggleButton* bTrash;
     Gtk::ToggleButton* bNotTrash;
     Gtk::ToggleButton* bOriginal;
+    Gtk::ToggleButton* bRecursive;
     Gtk::ToggleButton* categoryButtons[20];
     Gtk::ToggleButton* exifInfo;
     sigc::connection bCateg[20];
@@ -143,14 +151,15 @@ private:
     std::set<Glib::ustring> editedFiles;
     guint modifierKey; // any modifiers held when rank button was pressed
 
-    Glib::RefPtr<Gio::FileMonitor> dirMonitor;
+    std::vector<FileMonitorInfo> dirMonitors;
 
     IdleRegister idle_register;
 
     void addAndOpenFile (const Glib::ustring& fname);
     void addFile (const Glib::ustring& fName);
-    std::vector<Glib::ustring> getFileList ();
+    std::vector<Glib::ustring> getFileList(std::vector<Glib::RefPtr<Gio::File>> *dirs_explored = nullptr);
     BrowserFilter getFilter ();
+    void refreshDirectoryMonitors(const std::vector<Glib::RefPtr<Gio::File>> &dirs_to_monitor);
     void trashChanged ();
 
 public:
@@ -240,6 +249,7 @@ public:
     void setExportPanel (ExportPanel* expanel);
     void exifInfoButtonToggled();
     void categoryButtonToggled (Gtk::ToggleButton* b, bool isMouseClick);
+    void showRecursiveToggled();
     bool capture_event(GdkEventButton* event);
     void filterChanged ();
     void runFilterDialog ();