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/Query.cs

@@ -280,7 +280,7 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution
         /// <param name="startRow">The starting row of the results</param>
         /// <param name="rowCount">How many rows to retrieve</param>
         /// <returns>A subset of results</returns>
-        public Task<ResultSetSubset> GetSubset(int batchIndex, int resultSetIndex, int startRow, int rowCount)
+        public Task<ResultSetSubset> GetSubset(int batchIndex, int resultSetIndex, long startRow, int rowCount)
         {
             // Sanity check to make sure that the batch is within bounds
             if (batchIndex < 0 || batchIndex >= Batches.Length)