By Lucia Mutikani WASHINGTON (Reuters) -U.S. consumer confidence increased to a five-month high in December, with Americans growing more optimistic about current and future business conditions as well as the labor market, which could help to underpin the economy early next year. The jump in confidence reported by the Conference Board on Wednesday occurred across all age groups and household income levels. Though consumers continued to worry about inflation, many were planning to buy motor vehicles, houses and major appliances like refrigerators and clothes dryers over the next six months. More…