feature/edit/subset (#283)

* Changing query/subset API to only use Result on success, Error on error

* Creating an interservice API for getting query result subsets

* Updates to subset API

* RowStartIndex is now long
* Output of query/subset is a 2D array of DbCellValue
* Adding LongSkip method to LongList to allow skipping ahead by longs
* Moving LongList back to ServiceLayer utilities. Move refactoring

* Stubbing out request for edit/subset

* Initial implementation of getting edit rows

* Unit tests for RowEdit and RowDelete .GetEditRow

* Fixing major bugs in LongList implementation, adding much more thorough tests

* Adding some more unit tests and fixes to make unit tests pass

* Fixing comment

src/Microsoft.SqlTools.ServiceLayer/QueryExecution/Contracts/ResultSetSubset.cs

@@ -19,6 +19,6 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts
         /// <summary>
         /// 2D array of the cell values requested from result set
         /// </summary>
-        public string[][] Rows { get; set; }
+        public DbCellValue[][] Rows { get; set; }
     }
 }