* This was an oversight. The CMake conditional shall check for `TARGET`. However, even if this is fixed, `dune-testtools` does not allow to make tests over aliased targets because it wants to modify the `EXCLUDE_FROM_ALL` property. The solution is to use the unalised targets while dune-testtools solves the problem.
* Make exec targets available on main directory
* Make alias targets available on test directory
Add CHANGELOG

* There was a use of target_link_directories instead of target_include_directories.
* Executable targets were available but could not be compiled without its library.
* Dune dependencies are taken directly from its global variables. This enables MPI and UG_PARALLEL when necessary.
* The options file expected CMAKE_FLAGS and MAKE_FLAGS from environment, but dune-common happens to clear them before calling the options file. On this version, these are replaced by CMAKE_OPTIONS and MAKE_OPTIONS

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