#243 TSystemMessage overhaul

[Vidar Hasfjord]

Owlet [r6931] implements an overhaul of the utility class TSystemMessage:

NEW: Added member LangId and accessor GetLangId.
NEW: Added stream operator.
NEW: Added documentation.
CHG: Renamed class to TSystemError.
CHG: Removed member Message; message is no longer stored.
CHG: Removed member MessageBox; bloat.
CHG: Renamed member SysMessage to Format.
CHG: Renamed member SysError to GetError.
CHG: Removed member Init; now implemented in Format.
CHG: Passing an error code no longer calls SetLastError.
CHG: Now passes FORMAT_MESSAGE_MAX_WIDTH_MASK to FormatMessage to ignore newlines.
CHG: Now formats both error code and message, or just error code, if no message found.
CHG: Applied the class throughout Owlet, wherever GetLastError was formatted.

Please review.