Changed the roles of the header table, data table, and footer table to be "presentation" and changed the parent element of these tables to have role="grid".

Also changed all usages of the role "rowheader" to "row" because it was being used incorrectly. See http://www.w3.org/TR/wai-aria/roles#rowheader

These changes will provide better screen reader support. Tested with JAWS screen reader.