- replace string methods with property methods The class was originally adapted

- replace string methods with property methods The class was originally adapted
  from plib's file-picker, where it made some sense to keep the current path as
  string, and to chop off elements when leaving a dir, and adding them when
  entering. But it doesn't make the least sense in SGPropertyNode space, where
  we already have everything to move in a tree.

- add R & W flags for TRACE_READ and TRACE_WRITE. Remember: lower case letters:
  disabled (rw ... reading/writing), upper case letters: enabled (RWAUT)

- remove some verbosity & further cleanup ... to make further work easier :-)