Add SwipeDelegate::swipe.enabled

It would be nice, for example, in the Contact List example to have edit/remove swipe actions that are only accessible when a delegate is collapsed. When expanded, it can show the actions as buttons, like it currently does, and in that state it shouldn't be possible to swipe. It's probably already possible by assigning the components conditionally, but it would be nice if there was a simple swipe.enabled property to disable swipe in a specific state.