Allow Pagination of FindItem calls via IndexedPageItemView

Exchange 2010 and later added pagination support to allow for iterative processing of larger result sets and in fact it will refuse - depending on the server settings - to respond to requests that would return batches that are outside of the current limit, for us at least, this is a must have addition without which we could not use Viewpoint in production

Details for IndexedPageItemView here: 
http://msdn.microsoft.com/en-us/library/exchange/aa563549%28v=exchg.150%29.aspx

https://github.com/TobiG77/Viewpoint/commit/b35ef305966b73b0f375f2ff0567807d85472e0f