Fix display of nuxeo-data-table when a data-table-column is controlled by a dom-if template

Steps to reproduce :

1. start Nuxeo
2. replace nxserver/nuxeo.war/ui/document/workspace/nuxeo-workspace-view-layout.html by the attached "nuxeo-workspace-view-layout.html" file
3. log in as Administrator
4. navigate to the personal workspace
5. observe that the header "State" is displayed (without any content in the column) whereas this column is not selected in the settings
6. if other columns are added from the Settings popup, the same problem (with the extra header) will happen for all added columns

By looking at the HTML code of the page, it seems that the a DIV tag has been added inside the "nuxeo-data-table-cell" element.

Expected behavior: using nuxeo-data-table-column inside a "dom-if" template should work and not display any additional header or column