Makes distinction between functions more clear.

Currently, there are two abstract interface for the grids. One that
usually returns pods and arrays of them that also can be used by C
and is used also in opm-core, and one that returns Eigen datastructures
 needed within opm-autodiff.

This commit adds a postfix ToEigen to those functions (faceCells, and
cellCentroidsZ) one could imagine to also return pods and arrays of them.
This should at least resolve the confusion about the two faceCells functions.

The next step will be issue #192
Fixes #176
Add output of RS and RV to outputStateMatlab
Merge pull request #195 from totto82/rs_rv_output

Add output of RS and RV to outputStateMatlab
sim_fibo_ad*: change the default for the use_cpr parameter from false to true

SPE9 and Norne are basically unusable if UMFPack is used as linear solver...
Merge pull request #197 from andlaus/use_cpr

sim_fibo_ad*: change the default for the use_cpr parameter from false to...
Merge pull request #193 from blattms/fix-176

Makes distinction between functions more clear. (#176)