OPT show template/archetype items: add zero state with custom message when the OPT is disabled

[ppazos]

1. Go to templates
2. Click on one template
3. Disable the template
4. Go back to templates
5. Click on archetype/template items links
6. The list is empty because the "disable" action deleted the internal archetype nodes
7. Show a text mentioning the internal nodes were not indexed because the OPT is disabled