wx: Remove wxString implicit constructor from std::string

On windows, it uses the current system's character encoding instead of utf-8, which breaks a lot of things.  We should avoid it.

common/StringHelpers.cpp

@@ -31,6 +31,11 @@ __fi wxString fromUTF8(const char* src)
 	return wxString(src, wxMBConvUTF8());
 }
 
+__fi wxString fromUTF8(const std::string& str)
+{
+	return wxString(str.data(), wxMBConvUTF8(), str.size());
+}
+
 __fi wxString fromAscii(const char* src)
 {
 	return wxString::FromAscii(src);