Rework scripts for handling material data (crosssections)

[jhidding]

Rework means:

• translate C++ parts into Python
• move to HDF5 as intermediate storage, in stead of XML
• wrap Elsepa into Python interface
• Access ENDF data directly from Python
• Connect elements using Workflow techniques

[jhidding]

Interesting Python library: http://pyne.io/

[jhidding]

Using units in Python: https://pint.readthedocs.io/en/0.7.2/

[lvkessel]

See https://github.com/eScatter/cstool/tree/hdf5 and master...hdf5.