5b08de4244
they used to be in opm-core, but this allows to be more flexible with the dependency order: What's now called "opm-core" can easily depend on opm-material which might come in handy for the refactoring. Besides moving in classes from opm-core, the infrastructural code which was still in opm-material is moved to the directory opm/material/common. The intention is to collect these classes at a central location to make it easy to move them to a real "core" module. (if this is ever going to happen.)