L2 transforms publishes only salinity or density depending on whether they are salinity or density transforms

* L2 transforms publish granule containing only the physical variable they are for. Therefore, salinity transform only publishes salinity. Density transform only publishes density.

* Log debug statements have been added in the L2 transforms so that we can trace where the sea water algorithms may return NAN values for presumably unphysical input values for pressure, temperature etc present in the input granule.