Fix some problems on the options file and cmake

What does this MR do?

• 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

Is there something that needs to be double checked?

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Can this MR be accepted?

• I've read contribution guide
• Implemented
• Added/Updated tests
• Added/Updated documentation
• Pipelines passing

• Delete branch option set
• Fast-forwaded git merge is possible
• Added entry to CHANGELOG.md

Related issues

Closes #64 (closed)