The web browsers are quite tolerant to this but not the (x)html
validators. It is necessary to fix this for e.g. automatic web tests
not to fail.

* the contentCol carring layout information (class="col-dm-X")
  is now div#main-center instead of div#pageContent (see cset 1545a8e37c6c)

* HideLeftBar is renamed into HideAsidesBar

Follow up to commit 1c3434c6afd7.