replace the blackoil PVT classes by the ones of opm-material

the opm-material classes are the ones which are now used by
opm-autodiff and this patch makes it much easier to keep the opm-core
and opm-autodiff results consistent. Also, the opm-material classes
seem to be a bit faster than the opm-core ones (see
https://github.com/OPM/opm-autodiff/pull/576)

I ran the usual array of tests with `flow`: SPE1, SPE3, SPE9 and Norne
all produce the same results at the identical runtime (modulo noise)
and also "Model 2" seems to work.

tests/norne_pvt.data

@@ -5,11 +5,22 @@
 
 -- Copyright (C) 2015 Statoil
 
+RUNSPEC
 
 TABDIMS
 --ntsfun ntpvt nssfun nppvt ntfip nrpvt ntendp
    2     2     33     60   16    60 /
 
+DIMENS
+1 1 1 /
+
+GRID
+
+PROPS
+
+DENSITY
+      859.5  1033.0    0.854  /  Justert 22/7
+      860.04 1033.0    0.853  /  Justert 22/7
 
 PVTG