refactor(ui): standardize user variable naming and avoid a SQL query when only userID is used

- Use `user` everywhere, instead of sometimes `loggedUser`
- Delay the instantiation of some variables: no need to perform SQL queries for
  nothing.
- Remove a SQL query getting the whole user struct when only user.ID is used.

internal/ui/category_refresh.go

@@ -27,7 +27,6 @@ func (h *handler) refreshCategoryFeedsPage(w http.ResponseWriter, r *http.Reques
 }
 
 func (h *handler) refreshCategory(w http.ResponseWriter, r *http.Request) int64 {
-	userID := request.UserID(r)
 	categoryID := request.RouteInt64Param(r, "categoryID")
 	printer := locale.NewPrinter(request.UserLanguage(r))
 	sess := session.New(h.store, request.SessionID(r))
@@ -37,6 +36,7 @@ func (h *handler) refreshCategory(w http.ResponseWriter, r *http.Request) int64
 		time := config.Opts.ForceRefreshInterval()
 		sess.NewFlashErrorMessage(printer.Plural("alert.too_many_feeds_refresh", time, time))
 	} else {
+		userID := request.UserID(r)
 		// We allow the end-user to force refresh all its feeds in this category
 		// without taking into consideration the number of errors.
 		batchBuilder := h.store.NewBatchBuilder()