Improve handling of unicode paths etc.

[Angus Yeh]

First noticed the problem with Issue #84.

Loading of 'current directory' seems to fail when the path name contains strange characters (eg. the degree superscript circle in this case). see ui_main_window.py, loadSettings(), wd = str(s.value("current_directory", "").toString()). I might be able to try/except here. But maybe there is a better way to support unicode or things like that?

There are other places uses path, which is likely to have unicode strange names in new OS.

Maybe I should look for longer term solution by dealing with these paths correctly.