fixes #10526: Remove custom background on responsive tables and set it in the docs where it should've been originally

fixes #10521: Only remove bottom-border from last row of cells in tbody and tfoot within responsive tables

Fixed Table cell sizing with multiple classes by using *= instead of ^=

* Cuts  close to 100 lines of CSS from the table CSS
* File size aside, this drastically simplifies CSS for folks looking to
build on top of the `.table-bordered` option as a starting point

Needs work though—we shouldn't be setting this stuff with the attribute
selectors, but it's the easiest solution for now.

 This are already declare in normalize

* Removes text-align from td elements (no need to set that one)
* Specifically sets th to text-align: left; at a global level (no longer within .table) to override browser defaults
* Removes font-weight: bold; from th while we're at it since that's browser default already