refactor: Replace all occurencec of gtkmm.h and only use the necessary headers

include/util/chrono.hpp

@@ -5,7 +5,6 @@
 #include <functional>
 #include <condition_variable>
 #include <thread>
-#include <gtkmm.h>
 
 namespace waybar::chrono {
 

include/util/command.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <sys/wait.h>
+#include <giomm.h>
 
 namespace waybar::util::command {