correct one url and one type of entry

fix typos, named correct arguments of function calls, etc.

With the new structure, /ref bibliography doesn't work any more
on the mainpage. However, this solution only circumvents the problem.

added dois/urls so that doxygen can generate hyperlinks to the publications

The changing constitutive relations task in exercise 1 previously was about
exchanging the EffToAbsLaw with a LinearMaterial law. It makes more sense to
replace the RegularizedBrooksCorey.
The description in the handbook was adapted accordingly.

Fill missing entries in feature table

*Delete unused entries

Include new features, add links to models and test problems

Should even work when they stick to version 3.0, but
not vice versa.

Testing links for implicit models

*Fix errors
*Add .bib entry for citation

* Reduce number of template arguments
* Rename property from tau to TauTortuosity

Reviewed by heck

Instead of calculating it in the local residual, the effective permeability
is now calculated within a new file permeabilityrutqvisttsang.hh in the
folder dumux/material/fluidmatrixinteractions.
This is just one possible effective permeability model. Several others can be
added and set via the property EffectivePermeabilityModel.

Up to now, the permeabilities were averaged twice, first by calculating
the mean of the mean of the intrinsic permeabilities in the flux variables
and later by averaging the effective permeabilities in the local residual.
This is redundant. Now, only the mean of the effective permeability is
calculated in the local residual.
This change required to change the reference files for the sequential and
the parallel test.

* in handbook and doxygen
* add hint in the opts file