Council shall have the power to establish all offices and positions not otherwise provided for by this Charter which are necessary from time to time for the efficient conduct of the affairs of the Municipality. Council shall by ordinance fix all salaries and rates of compensation; but the salary or rate of compensation of an elected or appointed official, officer or employee who has been elected or employed for a definitely fixed period of time, shall not be increased or decreased during the term of office or appointment. All salaries and wage rates of employees of the Board of Municipal Utilities shall be approved by said Board before they are fixed by Council; and, unless and until changes in salaries and wages are so approved and modified by action of Council they shall remain as last fixed.