Add a collapse mode for large, responsive tables

It is very difficult to move through a table with a scroll bar on mobile screens. It would be better to make tables scale automatically (like TablePress tables do) and make that the default option. And for really large tables, offer a 'Collapse mode' to the responsive options, like the collapse mode that TablePress offers (see https://tablepress.org/extensions/responsive-tables/). This would make it much easier for visitors to browse large tables.