Show count of feeds with permanent errors in header menu

Only for feeds that reach `maxParsingError` are counted (so transient errors do not trigger counter).

ui/category_create.go

@@ -28,6 +28,7 @@ func (c *Controller) CreateCategory(w http.ResponseWriter, r *http.Request) {
 	view.Set("menu", "categories")
 	view.Set("user", user)
 	view.Set("countUnread", c.store.CountUnreadEntries(user.ID))
+	view.Set("countErrorFeeds", c.store.CountErrorFeeds(user.ID))
 
 	html.OK(w, r, view.Render("create_category"))
 }