make opm-porsol use the new opm-material module

I'm not sure whether it works, but I'm pretty sure that it compiles
and slightly less sure that the code is equivalent to what was there.
(it seems like the dumux material relations used so far were about two
years old, so there slightly more invasive changes were required to
the code.)
fix some config.h inclusion issues

- It seems like HAVE_CONFIG_H is not defined by the cmake build
  system, so config.h was not included in the files which used it.
- use quotes instead of pointy brackets to include config.h. That
  was inconsistent and I think that quotes better indicate the fact
  that the config.h is a project-local file.
Merge pull request #54 from andlaus/use-opm-material

Use the new opm material module

A practical fall-out from merging this change is that GCC 4.4 becomes 
the minimum supported target platform for OPM-Porsol and its downstream
modules such as OPM-Upscaling.