When the SolidEhlers ctor is not used it was not generated in the library.

Same function is used in Ehlers and in the LinearElasticIsotropic.

The different tangent types used for the tangent stiffness computation.

The main change was in the creation of liquid flow process;
the succeeding changes are just adoptation to a pointer,
instead of a reference with boolean.

This version checks if the PropertyVector is
assigned to the requested mesh item type and has
the required number of components.

The multiple inheritance for the phase field extension
is not actually needed and can be completely avoided.

This allows to store a const reference in the integratio
point data structures.

The function wraps the original createConstitutiveRelation()
function while checking the "id" attribute in the
<constitutive_relation id="0"> tag. The return value becomes
a map from int to constitutive relation pointers.

-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.

... and also comments.

* [CreepBGRa] Added a condition for the case of |s_try|=0

* [CreepBGRa] Compacted two lines into one by Dima's suggestion