The multidomain-lib and singledomain-lib are too generic to be set in any system, so this is replaced for something more specific

* This is header is removed for 2.8 and higher, tough

This makes more sensible name choices for exported target names, it manages installation components and fixes the test stage in CI 

* This changes allow to import and use targets by just finding the dune-copasi library. No dune library required for downstream project.
* The testing library may be used as a subfolder or as a dune-copasi downstream project.
* The config file is installed so that non-dune users may just include the config definitions without re-generation of the file.
* Python project not setup. It is not doing anything anyways.
* Updated dune module requirements to 2.7
* Adds basic information for CMake packaging

Now targets seem to be importable in a very simple manner.

* Library modes can be switched by default in CMake with the option BUILD_SHARED_LIBS
  hence no need to hardcode them with different targets.
* Exported targets were not working properly because the config file didn't contain enough
  information (DUNE creates one by default). So I remove it and will refactor all CMakeFiles
  later to use modern CMake directly (without DUNE macros).