Make swipe stuff public

Namely HdySwipeTracker and HdySwipeable.

• !517 (merged)
• Add a way to fix #167 (closed), because we won't be able to change it later
• Write proper docs for HdySwipeable
• Write proper docs for HdySwipeTracker
• Make HdySwipeable fully public, bump versions to 1.0
• Make HdySwipeTracker fully public, bump versions to 1.0
• Introduce hdy_swipeable_get_swipe_tracker() and stop using g_object_set_data() magic. This needs to be done at the end after they are both public