Make it possible to use CMAKE instead of autotools for build process

[fangohr]

Currently, we use autotools in the spack/package.py.

Octopus 14.0 provides support for CMake as the build system. This issue is to modify the spack package for Octopus to support CMake as the build system.

Ideally, the user has a choice wether to build [email protected] with autotools or CMake, but the vision for the future appears to be a purely CMake-based build. So if necessary, we can switch to CMake-only builds from 14.0 (if already possible) or from a later version of Octopus (if CMake support doesn't match the autotools support for the dependencies available through spack).