* Add optional dependencies TBB and ParallelSTL. Update CMake configuration to
  handle native ParallelSTL support by the standard library.
* Add TBB to base Docker image and update image version.
* Add `ParallelExecution` interface for controlling multithreading during runtime.
* Add STL algorithm overloads using Utopia::ExecPolicy.
* Integrate multithreading settings into meta-config and model setup.
* Add tests for parallel setup and algorithms and extend `apply_rule` test with
  test case for parallel execution enabled.
* Add parallel features to Doxygen docs and Utopia Feature List.
* Update README.md
* Revert commit dd498922, reversing changes made to ba64cc5d.