update/fix handling of NLS and TS solver statuses in Problem
update/fix handling of NLS and TS solver statuses in Problem

- update .set_solver(), .init_solvers(), .solve()

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