Add return type annotations to Zonal Summary Methods
Fix TiledPolygonalZonalSummarySpec to work with DataSource changes
Merge pull request #613 from ejc123/ZonalSummaryFix

Add return type annotations to Zonal Summary Methods
Merge pull request #614 from ejc123/FixZonalSummarySpec

Fix TiledPolygonalZonalSummarySpec to work with DataSource changes