[FIX](ValueLabelVar toString) Correctly converting null values to ""
[FIX](Scene format) Regression in obtaining the scene atoms value; now using #firstAtoms instead of #atoms.
[CHG](HeatGrid valuesVisible) When UseShapes=true, the new default value of valuesVisible is false.
[FEAT](HeatGrid valuesMask) ValuesMask property is now supported
[IMP](HeatGrid) Code cleanup.