Allow a caller to ignore row numbers

For calls to readCoordinates, read, and slice the returned value order
in the `Data` response is the same as requested.  While having the row
numbers included in the response is convenient, when the number of cells
being returned is high this incurs memory and serialization overhead.
This is especially true when retrieving a small number of columns for a
large number of rows; in this case `rowNumbers` can actually be more
expensive to include than the data itself.

Here we use the Ice context and "omero.tables.include_row_numbers" to
additively affect the client API without changing any of the Ice method
prototypes.

src/omero/hdfstorageV2.py

@@ -550,13 +550,21 @@ def getWhereList(self, stamp, condition, variables, unused,
             aue.serverExceptionClass = str(err.__class__.__name__)
             raise aue
 
-    def _as_data(self, cols, rowNumbers):
+    def _as_data(self, cols, rowNumbers, current):
         """
         Constructs a omero.grid.Data object for returning to the client.
         """
+        include_row_numbers = True
+        try:
+            include_row_numbers = current.ctx.get(
+                "omero.tables.include_row_numbers", "true"
+            ).lower() == "true"
+        except Exception:
+            pass
         data = omero.grid.Data()
         data.columns = cols
-        data.rowNumbers = rowNumbers
+        if include_row_numbers:
+            data.rowNumbers = rowNumbers
         # Convert to millis since epoch
         data.lastModification = int(self._stamp * 1000)
         return data
@@ -568,7 +576,7 @@ def readCoordinates(self, stamp, rowNumbers, current):
         cols = self.cols(None, current)
         for col in cols:
             col.readCoordinates(self.__mea, rowNumbers)
-        return self._as_data(cols, rowNumbers)
+        return self._as_data(cols, rowNumbers, current)
 
     @stamped
     def read(self, stamp, colNumbers, start, stop, current):
@@ -586,7 +594,7 @@ def read(self, stamp, colNumbers, start, stop, current):
         elif start is None and stop is None:
             rowNumbers = list(range(self.__length()))
 
-        return self._as_data(cols, rowNumbers)
+        return self._as_data(cols, rowNumbers, current)
 
     @stamped
     def slice(self, stamp, colNumbers, rowNumbers, current):
@@ -604,7 +612,7 @@ def slice(self, stamp, colNumbers, rowNumbers, current):
             col = cols[i]
             col.readCoordinates(self.__mea, rowNumbers)
             rv.append(col)
-        return self._as_data(rv, rowNumbers)
+        return self._as_data(rv, rowNumbers, current)
 
     #
     # Lifecycle methods