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/EditData/UpdateManagement/CellUpdate.cs

@@ -85,6 +85,22 @@ namespace Microsoft.SqlTools.ServiceLayer.EditData.UpdateManagement
 
         #region Properties
 
+        /// <summary>
+        /// Converts the cell update to a DbCellValue
+        /// </summary>
+        public DbCellValue AsDbCellValue
+        {
+            get
+            {
+                return new DbCellValue
+                {
+                    DisplayValue = ValueAsString,
+                    IsNull = Value == DBNull.Value,
+                    RawObject = Value
+                };
+            }
+        }
+
         /// <summary>
         /// The column that the cell will be placed in
         /// </summary>