Add edit/delete actions to the news list and detail pages

Both gated the same way editing already was: broad while a draft,
editor/admin-only once published. The list's Edit link goes to the
detail page rather than straight to the edit form, matching the
member list's convention.

management/context_processors.py

@@ -53,6 +53,7 @@ _NAV_SECTIONS = {
     "news_create": "news_list",
     "news_detail": "news_list",
     "news_update": "news_list",
+    "news_delete": "news_list",
     "news_publish": "news_list",
     "news_unpublish": "news_list",
     "news_photo_upload": "news_list",