(ScrollView) Panning is disabled if ScrollTo is called while panning

[problem]     If application calls ScrollTo while we're panning we go into an incorrect state.
[cause]       When we're panning, and the application calls ScrollTo, swiftly followed by a call
              to disable scroll-sensitivity, the panning value is never cleared.
              When scroll-sensitivity is enabled, we start animating to a wrong position.
              Also trying to use the property value when we set sensitivity which can be out-of-date.
[solution]    Clear the panning value when we want to animate to another position.
              Use event-side panning value when changing scroll-sensitivity.

Change-Id: I3cc2200839ad3a2ec1fc705f542bd8df41502462
Signed-off-by: Adeel Kazmi <adeel.kazmi@samsung.com>