Update lib/gui_qt.py

Replaced white spaces that are at the end of the phrase and after a dot.

_('example of a text string to be translated. ')

This white space at the end is not recognized in the translation wiki so that string is not added to the translations files, then the text string is not translated in the GUI.

_('example of a text string to be translated.') + ' '

This is solved by adding the white space in a separate string. So it has to be done this way in future added text strings to this file to avoid future translation bugs.