write out the reservoir state to the eclipse binary format

most code was shamelessly ripped from opm-core's EclipseGridParser,
but there are some additions (e.g. grids specified using the D[XYZ]V
Eclipse keywords can be used).

The code is located inside the new class "BlackoilEclipseOutputWriter"
(should probably renamed) and hooked up in
SimulatorFullyImplicitBlackoil and sim_fibo_ad.cc.

Also be aware that, to make this code work properly, the newest master
version of ERT is required (i.e. one which includes commit
5e4e9661720). In this context, I would like to thank Joakim Hove for
his support!