. . . "3-1-1 Except as otherwise provided by this charter, all executive powers of the town shall be vested in the board of selectmen, which shall have all the powers and duties given to boards of selectmen under the constitution and General Laws and such additional powers and duties as may be authorized by this charter, by by-law or by town meeting vote. 3-1-2 The board of selectmen shall serve as the g" .