Fixed prototype detection

See merge request !80

Improved system_type detection

See merge request !77

Updated the AFLOW prototype data. The new data is stored within nomad-FAIR instead of using the one in nomadcore. Modified systemnormalizer to use this new data through the new structure.py module that is created for handling various structure-related tasks.

Added access to the backend data through bracket notation (simplifies access syntax). Added test for getting representative systems for molecular dynamics and geometry optimization.