adapt to the new opm-material file names
add opm-core to the dependencies in dune.module

actually, this is not really required as opm-material already
specifies the dependency and ewoms does not use opm-core directly. In
the future the second point may change, so it is probably a good idea
to add it...
add opm-core to the ewoms prerequisites
some renames to draw the eWoms directory structure nearer to the the one of the remaining OPM modules

this renames the 'test' directory to 'tests' and 'test/implicit' to
'tests/models'. the latter change reflects the fact that in eWoms all
models are implicit since the IMPET models have been removed.
use opm property system, improvments to the parameter system
adapt the tutorial and the handbook to the brave new world

we do not have a decoupled tutorial anymore since, well, the decoupled
models have been removed. Also since the move to the Opm CMake based
build system, the "How to create a new folder" section in the handbook
was obsolete.
Extracts the full compiler path and feeds it to cmake.

Previously, specifying the compiler name with a variable
to configure ("configure CC=gcc") lead to CMake complaining
that <builddir>/$CC was not a valid path. This patch fixes
this by extracting the full path with "which <compiler>".
Should fix issue #355.
substituted which with command -v.
Change which test for cmake28 to use command -v.
Test for executable and preserve erroneous path for messages

If an alternate compiler is specified, then check if this is actually
executable before assigning it so that we don't end up with specifying
an empty name to CMake. If the path does not exist, it will be preserved
so that CMake will complain with an easily identifiable error message.
get rid of math.hh and the tabulated 2D function code

math.hh can be replaced by opm/core/utility/Average.hpp and the
tabulated 2D functions are now part of opm-material.