Added delegate callback to detect when panning is finished, to potent…

…ially allow users to manually reset the hightlight values once panning is complete

Source/Charts/Charts/BarLineChartViewBase.swift

@@ -779,6 +779,8 @@ open class BarLineChartViewBase: ChartViewBase, BarLineScatterCandleBubbleChartD
                 }
 
                 _isDragging = false
+
+                delegate?.chartViewDidEndPanning?(self)
             }
 
             if _outerScrollView !== nil

Source/Charts/Charts/ChartViewBase.swift

@@ -25,6 +25,9 @@ public protocol ChartViewDelegate
     /// - parameter highlight: The corresponding highlight object that contains information about the highlighted position such as dataSetIndex etc.
     @objc optional func chartValueSelected(_ chartView: ChartViewBase, entry: ChartDataEntry, highlight: Highlight)
 
+    /// Called when a user stop highlighting values while panning
+    @objc optional func chartViewDidEndPanning(_ chartView: ChartViewBase)
+
     // Called when nothing has been selected or an "un-select" has been made.
     @objc optional func chartValueNothingSelected(_ chartView: ChartViewBase)