MOSCOW (Reuters) - President Vladimir Putin offered couples cash to have more children to halt a dramatic decline in population and called for a stronger army in a key speech on Wednesday in which he shrugged off sharp attacks by Washington. Putin, defying predictions he would focus on foreign policy, zeroed in on Russia's dwindling population -- an issue with huge implications for the economy -- which is falling by 700,000 people every year. In his annual speech to the nation, the president, who in July hosts leaders of the G8 group of rich democracies, responded only obliquely to stinging...