Adds fully implicite black oil solver working with CpGrid

This is #90 rebased for the current master.

This pull request uses the corresponding pull request OPM/opm-core#518, and OPM/dune-cornerpoint#72 and adds a variant (examples/sim_fibo_ad_cp.cpp) of a fully implicite black oil solver that uses CpGrid instead of UnstructuredGrid.

As a consequence dune-cornerpoint becomes a suggestion for opm-autodiff
The patches are tested with an SP1 example that Atgeirr provided me with. It seems like one gets the same results as with UnstructuredGrid. As we use the VTKWriter of DUNE for output and need the parallel version to pass it a path, the produced file names are different.

 Buildsystem changes in commit e1e9e677a344c0361d038555ef1de2eb5320f0a0 need to be applied to opm-core, too.

Please note that parts of the contents of opm/autodiff/GridHelpers.[hc]pp should probably be move to dune-cornerpoint for broader use.