An Act to Permit the Washington Convention Center Authority to Expend Revenues for the Operation and Maintenance of the Existing Washington Convention Center and for Preconstruction Activities Relating to a New Convention Center in the District of Columbia, to Permit a Designated Authority of the District of Columbia to Borrow Funds for the Preconstruction Activities Relating to a Sports Arena in the District of Columbia and to Permit Certain Revenues to Be Pledged as Security for the Borrowing of Such Funds, and for Other Purposes