Wiki column updates to better manage RTL and hidden columns

The PR dreams are made of.  I was tripping over wiki issues when in RTL mode when the subnav column was hidden.  Turns out, if I simply remove the column from the DOM when hidden, the column container's :last-child rules kick in and I can avoid all that.

This PR looks big but isn't.  I was wrapping all of the homepage stuff in #home but that just bloats the CSS so I moved most of it out.

Would love to get this PR merged by end of day so Jean-Yves doesn't needlessly open tickets for a few things tomorrow.