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

Replaced old system type test with new one that currently tests bulk and 2D systems. Fixed the file fcc_crystal_structure.json that had the cell given in angstroms instead of meters. This was the reason for the oddities in the old system type test - the supposed to be bulk structure was categorized as atom because the atoms were meters apart.

DOS normalizer: (1) fixed wrong handling of <<single_configuration_calculation>> indices. (2) Added <<dos_values_normalized>> to public.nomadmetainfo.json. (3) added a new data file for DOS testing: <<tests/data/parsers/vasp/vasp_dos.xml>>. (4)  Codestyle/Lint checks passed locally.

Added actual parsers qbox, fleur, molcas,  dmol. Other parser related fixed. Processing catching sys.exit in tasks and parsers.

Updated normalizers to use Matid and combined symmetry, system type and system normalizers into one normalizer.