Update ListViewItem.cs

Implement interface IDataItemContainer
Update ListViewItem.cs

Share index between DataItemIndex and DisplayIndex properties
Update ListViewItem.cs

Wrap .NET 4 logic within NET_4_0 macro
Update ListViewItem.cs

Made new properties public
Update ListViewItem.cs

Fixed mistakes in previous commits
Update ListViewItem.cs

Make properties public (again)
ListViewItem class now implements interface IDataItemContainer
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