Added UIEdgeInsets property for selection indicator

Now able to control selection controller horizontal/vertical position offsets through a public property.

Note: This does not affect the bounding box of HMSegmentedControlSelectionStyleBox
• When HMSegmentedControlSelectionIndicatorLocationUp is selected, bottom edge insets are not used
• When HMSegmentedControlSelectionIndicatorLocationDown is selected, top edge insets are not used