Visitor implementations complete.

1. The SQL command text is converted to an ICommand object using SQL Generation (as before)
2. The old code that Manually navigated over the structure of ICommand (using a lot of casting) to build the appropriate Xrm organisation request message has now been replaced with some new "Visitor" implementations - which take advantage of the Visitor design pattern (recently implemented in SQL generation). These new visitors visit the ICommand and build the appropriate Xrm SDK request message:-
    * CreateRequest
    * RetrieveMultipleRequest
    * UpdateRequest
    * DeleteRequest