Added call to iOS api to reset separator insets

Details in [Jira ticket](https://jira.appcelerator.org/browse/TIMOB-17676)

In iOS 8, there is one new property for all the objects inherit from UIView. So, the solution to set the SeparatorInset in iOS 7.x will not be able to remove the white space you see on the UITableView in iOS 8.

The new property is called "layoutMargins".