Resolves #139, crash on Autolayout code due to constraints

This resolves the crash on iOS 6 and has no impact on iOS 7+.

Ideally, we think it might be best to rethink the view hierarchy and NOT move the contentView out of the UITableViewCell root, but instead pull the subviews out and place those in the ScrollView.  That would require substantial reworking though so we opted for this in the near term.

Hopefully this will help some other folks in the mean time.
Great library!
MV