since dune.module is primarily required for dunecontrol support and
you cannot run dunecontrol without dune-common anyway, nothing changes
for dunecontrol users.
for users who do not use dunecontrol, nothing changes either because
the dependencies are specified in opm-common-prereqs.cmake which stays
untouched by this commit.
since the opm-cmake does not contain any source files, placeholder
versions of the configure bash script and Makefile are
sufficient. These files are required because dunecontrol calls
'./configure' and 'make' unconditionally. (Also, the downstream
modules need to depend on opm-cmake to find the build macros...)
