By Guy Faulconbridge MOSCOW (Reuters) -President Vladimir Putin has warned the West that Russia could use nuclear weapons if it was struck with conventional missiles, and that Moscow would consider any assault on it supported by a nuclear power to be a joint attack. Here are key facts about Russia’s nuclear arsenal: HOW MANY NUCLEAR WEAPONS DOES RUSSIA HAVE? Russia, which inherited the Soviet Union’s nuclear weapons, has the world’s biggest store of nuclear warheads. […]