Modify EditBox for win32

1. Do render when the system DialogBox popup
2. '*' wll be shown in win32 edit control if the EditBox's input flag is
password
3. Function editBoxTextChanged will be called when the text in win32
edit control is changed
4. Return value std::string is a temporary variable, that may destruct
when AnsiToUtf8(...).c_str() or Utf8ToAnsi(...).c_str()