This allows writing components using cwtags which monkeypatches
CubicWeb's UStringIO for correct operations.

This fixes a regression introduced by commit 45b3eb604765.

Fixes a regression introduced by commit 530993d25fe5.

[components] `content_components` (e.g `rqlinput` and `applmessages` components) must be placed before the `div.pageContent` to avoid them vanish after `div.pageContent` reloaded.

closes #3905675

* 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.

* remove useless classes and id
* add aria-roles

(closes #3553532)

clean the TheMainTemplate