Implement file naming according to coding standard.

[jcartus]

PEP-8 dictates all modules and packages to be lowercase in file name. If necessary underscrores can be used to improve readability. See also here: https://www.python.org/dev/peps/pep-0008/#package-and-module-names

This mainly affects:

• NeuralNetworkUtilities in src/.
• files in src/data_generation.
• files in examples/

Edit in branch "restructure"!

[ralf-meyer]

GRaz Atomic Neural Networks for Interpolation of Energy Surfaces