Real and personal estate, except U.S. public money, held by a town in trust for any purpose, including cemetery trust funds, unless the person giving the same otherwise directs, shall be under the charge and management of three trustees, elected by the town when the town so votes. At the meeting when such trustees are first elected, they shall be elected for the following terms: one for one year, one for two years, and one for three years. Their successors shall be elected for the term of three years, but a person chosen to fill a vacancy caused by death, resignation, or otherwise shall serve only for the remainder of the unexpired term.