Fix most of critical issues reported by Sonar (GTK client) (#2309)

* (C++) Macros should not be used to define constants

* (C++) Memory should not be managed manually

* (C++) "void*" should not be used in typedefs, member variables, function parameters or return type

* (C++) When the "Rule-of-Zero" is not applicable, the "Rule-of-Five" should be followed

* (C++) "switch" statements should have "default" clauses

* (C++) "explicit" should be used on single-parameter constructors and conversiosn operators

* (C++) Non-const global variables should not be used

gtk/OptionsDialog.cc

@@ -31,13 +31,13 @@
 namespace
 {
 
-#define N_RECENT 4
+auto const MaxRecentDestinations = size_t{ 4 };
 
 std::list<std::string> get_recent_destinations()
 {
     std::list<std::string> list;
 
-    for (int i = 0; i < N_RECENT; ++i)
+    for (size_t i = 0; i < MaxRecentDestinations; ++i)
     {
         auto const key = gtr_sprintf("recent-download-dir-%d", i + 1);
 
@@ -65,8 +65,8 @@ void save_recent_destination(Glib::RefPtr<Session> const& core, std::string cons
     /* add it to the front of the list */
     list.push_front(dir);
 
-    /* save the first N_RECENT directories */
-    list.resize(N_RECENT);
+    /* save the first MaxRecentDestinations directories */
+    list.resize(MaxRecentDestinations);
     int i = 0;
     for (auto const& d : list)
     {
@@ -88,6 +88,8 @@ class OptionsDialog::Impl
 public:
     Impl(OptionsDialog& dialog, Glib::RefPtr<Session> const& core, std::unique_ptr<tr_ctor, void (*)(tr_ctor*)> ctor);
 
+    TR_DISABLE_COPY_MOVE(Impl)
+
 private:
     void sourceChanged(Gtk::FileChooserButton* b);
     void downloadDirChanged(Gtk::FileChooserButton* b);