sys: Tons of long overdue cleanup

- std::string -> const std::string& where needed
- Added a FileIO abstraction class
- Fixed recent files not updating
- Removed localization file from global include
- Renamed lang to pattern_language/pl
- Renamed EventFileDropped to RequestFileOpen

source/init/tasks.cpp

@@ -5,7 +5,7 @@
 
 #include <hex/helpers/net.hpp>
 #include <hex/api/content_registry.hpp>
-#include <hex/lang/pattern_data.hpp>
+#include <hex/pattern_language/pattern_data.hpp>
 
 #include <fontawesome_font.h>
 #include <codicons_font.h>