Municipalities shall have the right and power to frame and adopt home rule charters. Adoption, amendment or repeal of a home rule charter shall be by referendum. The General Assembly shall provide the procedure by which a home rule charter may be framed and its adoption, amendment or repeal presented to the electors. If the General Assembly does not so provide, a home rule charter or a procedure for framing and presenting a home rule charter may be presented to the electors by initiative or by the governing body of the municipality. A municipality which has a home rule charter may exercise any power or perform any function not denied by this Constitution, by its home rule charter or by the General Assembly at any time.