mainwindow: update range upon rate update

Range depends on rate. So update the range combo box upon change of
the rate combo box.
settings: adjust min combo/spin width to label width

If there are labels longer than the actual contents within the
related combo/spin box, then we want its width to be increased to
the label width.
de_DE: update German translation

The elements display, rate and range need translations. Furthermore,
some translations have been moved to settings.