* Make KuiTable headers keyboard-accessible in UI Framework.
* Use flexbox to consistently apply spacing between table header cell text and sort icon.
* Add aria-label attributes to KuiTableHeaderCell, KuiTableHeaderCheckBoxCell, and KuiTableRowCheckBoxCell.
* Update Jest snapshots.
* Update Dashboard listing table with new markup.
* Update Saved Objects tables with new markup.
* Update Settings table with new markup.
* Update Visualize listing table with new markup.
* Remove padding-right for cells containing checkboxes.
* Update sortableColumn directive with new markup.