UIRefreshControl-like behavior

[bondareb-evgenii]

Split loading state to one while dragging and after the user releases his finger. Now control starts animating and sends update request just after the user scrolls enough down while he is dragging. Both cases of releasing before finishing and after it. Fixed loading animation (slight jumping) on iOS 11. Added .top default value to Position params

[rnkyr]

hey, @bondareb-evgenii sorry for a late response and thank you for your contribution! please resolve conflicts so I can merge your pr