In enyo.Panels, ensure that we report the right index value to observers

In enyo.Panels, we clamp the index value to ensure that it is being set to something legal. We also forcibly notify observers whenever index is set (regardless of whether the value has actually changed). In cases where the provided value has been clamped, we have been reporting the wrong (unclamped) value to observers. This change addresses this issue.

Enyo-DCO-1.1-Signed-Off-By: Gray Norton (gray.norton@lge.com)