* fixed clang warning

 * optimized Node::sufficientForBody

  * delete dead code
  * fix further cppcheck hints

  * find useful names

  * (added boost dependency)

  * increase number of iterations to get reasonable long runtime

  * use std::all_of Tree::isCorrect()
  * refactoring

 * use unique_ptr for BarnesHutTree

 * removed unused virtual function declarations

 * fix clang-tidy warnings

 * use iterators more extensively

  * do squared comparison instead of sqrt
  * remove unused Node::parent
  * forwarding reference optimization for MPI send

  * removed unnecessary this pointer qualifier when accessing members