This patch refactors (hopefully) all parts of opm-core that are needed
by the fully implicite black oil solver in opm-autodiff and that inherently
relied on UnstructuredGrid.
We added a new simple grid interface consisting out of free functions
that will allow us to use CpGrid without copying it to an UnstructuredGrid
by the means of the GridAdapter. Using this interface we have add methods that
allow specifying the grid information (global_cell, cartdims, etc.) wherever
possible to prevent introducing grid parameters for the type of the grid.
Unfortunately this was not possible everywhere.
for some of these files this is needed to make to keep it compiling
after the next patch because the new ErrorMacros.hpp file will no
longer implicitly includes <iostream>. for the remaining files it is
just good style.
While at it, the includes for most of these files have been ordered in
order of decreasing abstraction level.
