Changes str.format() to (%s) % (str): fix for non-ascii chars

I am aware this going to break the translation files, but it is necessary to avoid the ```UnicodeEncodeError``` if non ascii chars are used in path file or directory.
Changing ```str.format()``` to ```u'str'.format()``` works but it seems not applicable to ```QCoreApplication.translate()```.

So, if someone knows any solution to avoid to break the translation file please let me know it !

Thanks!