Fix page admin layout

When editing pages with zones missing, zones were added to the bottom instead of the order of the page template.

"cols" and "rows" information was missing for existing page zones (as it is not persisted). Now that information is copied explicitly.

"cols" were translated to "colspan" in a table layout, but columns got their width mostly dictated by the content. By using "table-layout: fixed" the layout is following the "cols" structure.