implement support for the NTG, MULTPV, and MULT[XYZ]-? keywords

or rather grid properties, since they can be edited using MULTIPLY and
friends. note that the property interfaces must be extended for this
because EclipseState is not passed to the DerivedGeology class and is
not even available in some cases...

this PR depends on the OPM/opm-core#610
> depends on coordinate system.

Correct.  The coordinate system in ECL is right-handed with the origin in the upper left back corner, the X axis pointing right, the Y axis pointing forwards and the Z axis pointing down.