button: Add AButton class

The AButton class is designed as full a substitute to ALabel. The
GtkButton attribute 'button_' is initialized with a label. This
label can the be referenced by the subsequent inheritors of AButton
instead of the GtkLabel attribute 'label_' of ALabel.
For convenience a GtkLabel* 'label_' attribute is added to AButton.

If the button cannot be clicked it is disabled, effectively acting
like its label predecessor.

GtkButton seems to catch one-click mouse events regardless of the
flags set on it. Therefore, 'signal_pressed' is connected to a
function creating a fake GdkEventButton* and calling 'handleToggle'
(for details on this possible bug in GTK see:
https://stackoverflow.com/questions/45334911 )

In accordance with other GtkButtons (i.e. the sway/workspace ones)
set_relief(Gtk::RELIEF_NONE) is called on the 'button_' instance.

include/modules/hyprland/language.hpp

@@ -1,20 +1,20 @@
 #include <fmt/format.h>
 
-#include "ALabel.hpp"
+#include "AButton.hpp"
 #include "bar.hpp"
 #include "modules/hyprland/backend.hpp"
 #include "util/json.hpp"
 
 namespace waybar::modules::hyprland {
 
-class Language : public waybar::ALabel {
-public:
+class Language : public waybar::AButton {
+ public:
   Language(const std::string&, const waybar::Bar&, const Json::Value&);
   ~Language() = default;
 
   auto update() -> void;
 
-private:
+ private:
   void onEvent(const std::string&);
 
   void initLanguage();
@@ -26,4 +26,4 @@ private:
   std::string layoutName_;
 };
 
-}
+}  // namespace waybar::modules::hyprland