quick-add-popover: focus entry after calendar selection

Pressing 'Enter' key shall always save the event.
So focusing on 'Add' button after selecting calendar is redundant.

Instead, focus on the entry, so that the user can add more text without
manually focusing.

https://bugzilla.gnome.org/show_bug.cgi?id=778373

src/gcal-quick-add-popover.c

@@ -204,8 +204,8 @@ select_row (GcalQuickAddPopover *self,
   /* Return to the events page */
   gtk_stack_set_visible_child_name (GTK_STACK (self->stack), "events");
 
-  /* Focus back the "Create" button */
-  gtk_widget_grab_focus (self->add_button);
+  /* Focus back the event Entry */
+  gtk_entry_grab_focus_without_selecting (GTK_ENTRY (self->summary_entry));
 
   g_clear_object (&circle_pixbuf);
 }