fix default plot_kwargs in Log.add_group()
fix default plot_kwargs in Log.add_group()

sfepy/sfepy,BubuLK/sfepy,rc/sfepy,vlukes/sfepy,rc/sfepy,BubuLK/sfepy,sfepy/sfepy,rc/sfepy,vlukes/sfepy,BubuLK/sfepy,vlukes/sfepy,sfepy/sfepy