[T] HC Tests updated

-elder benchmark updated

-heterogenous HC benchmark reference files updated

-goswami benchmark temporarly removed from HC-tests

-SimplySynthetics: ConcentrationAndDiffusionOnly needed small changes in .prj file

-SimpleSynthetics: Project file adapted

-SimpleSynthetics :DiffusionAndStorageAndAdvection modified. Variable density model (p and c dependant) added, non boussinesq effects observed, consistency check,
		update of reference files

-SimpleSynthetics: DiffusionAndStorageAndGravityAndDispersionHalf- A new project has been set up, since the old setup was not converging anymore due to too large
		differences in density leading to problems in non boussinesq treatment.

-SimpleSynthetics: DiffusionAndStorageAndAdvectionAndDispersion- reference files updated. _max iter value in project file sligthly increased.

-SimpleSynthetics: DiffusionAndStorageAndAdvectionAndDecay- reference files updated. density model in prj file changed in order to account for storage.

-SimpleSynthetics: DiffusionAndStorageAndAdvectionAndDispersionHalf- reference files updated. density model in prj file changed in order to account for storage.