Oktavian Benchmark Implementation

[davidepettinari]

This pull request adds the Oktavian benchmark implementation for tungsten and aluminum. The implementation is up-to-date, and additional elements (Co, Cr, Cu, LiF, Mn, Mo, Si, Ti, Zr) will be included soon. The model is consistent with the other existing models.

The results database includes:

• Experimental results.
• MCNP 6.1.1b results using JENDL-4.0, TENDL-17, ENDF/B-VIII.0, and JEFF-3.3 libraries.
• OpenMC v0.14.0 results using ENDF/B-VIII.0, JEFF-3.3, and FENDL-3.2 libraries.

In the 'oktavian_w' folder, results with the FENDL-3.2 library will be added shortly to complete the benchmark.
The 'oktavian_al' folder contains MCNP 6.1.1b and OpenMC 0.14.0 results with the ENDF/B-VIII.0 library, along with corresponding experimental data.

[SteSeg]

Hi Davide! thank you for the implementation!
Just one thing:

According to PR #22 the arguments of the ResultsFromDatabase class constructor will be soon changed from filename and path to just file that contains a complete string with the path of the file. Could you update your PR according to this as soon as PR #22 gets merged?