Port extractor to TBB
Replace omp atomic with std variant
Port StaticRTree to use TBB
Port Contractor to TBB
Set number of threads in TBB
Use append operator instead of function, because function is inplace.
Set requested threads in TBB
Add TBB to travis.ymk
Make some temporary variables const
Merge pull request #1028 from TheMarex/tbb-port

Port from OpenMP to TBB