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

plugins/windows/source/lang/en_US.cpp

@@ -1,4 +1,5 @@
 #include <hex/api/content_registry.hpp>
+#include <hex/helpers/lang.hpp>
 
 namespace hex::plugin::windows {