By Andrew Osborn LONDON (Reuters) – Jailed Kremlin critic Alexei Navalny on Tuesday used the second anniversary of his incarceration to reinforce his promise to keep opposing the Kremlin, as his family and allies launched a campaign to free him. Navalny, 46, was arrested exactly two years ago as he returned to Russia from Germany, where he had been treated for poisoning with a deadly Soviet-era nerve agent in what he and some Western nations said was a Russian state assassination attempt. The Kremlin denied involvement. “Our miserable, exhausted Motherland needs to be saved. It has been pillag…