Fix table presentation in IE6-8

IE6-8 do not support :first-child and :last-child pseudo selectors.
Add fallback classes to first and last table columns and style those
correctly. Fallback styles need to be fully separated from pseudo class
rules as IE ignores the fallback style otherwise.
Merge pull request #180 from alphagov/fix-55878868-failures-table

Fix table presentation in IE6-8