Rename taxonomy kinds from taxonomy to term, taxonomyTerm to taxonomy

And we have taken great measures to limit potential site breakage:

* For `disableKinds` and `outputs` we try to map from old to new values if possible, if not we print an ERROR that can be toggled off if not relevant.
* The layout lookup is mostly compatible with more options for the new `term` kind.

That leaves:

* Where queries in site.Pages using taxonomy/taxonomyTerm Kind values as filter.
* Other places where these kind value are used in the templates (classes etc.)

Fixes #6911
Fixes #7395

hugolib/page__paginator.go

@@ -89,7 +89,7 @@ func (p *pagePaginator) Paginator(options ...interface{}) (*page.Pager, error) {
 			// section. To avoid the default paginators for the home page
 			// changing in the wild, we make this a special case.
 			pages = p.source.s.RegularPages()
-		case page.KindTaxonomy, page.KindTaxonomyTerm:
+		case page.KindTerm, page.KindTaxonomy:
 			pages = p.source.Pages()
 		default:
 			pages = p.source.RegularPages()