improvements w7_defects/crystalline_defects

[basnijholt]

trafficstars

• sorting_mid argument is not used in get_densities
• box is missing in density plots, compare with edx_2015
• create_edge_dislocation_system and create_screw_system can be combined and would simplify the plotting

[basnijholt]

Also awkward way of generating parameters:

    parameters = {
        'BHZ': {'A': 1.0, 'B': 1.0, 'D': 0.0, 'M': 0.8},
        'QAH': {'A': 1.0, 'B': 1.0, 'D': 0.0, 'mu': 0.8}}

    p_BHZ = SimpleNamespace(field=.005, t_inter=-.1, **parameters['BHZ'])
    p_QAH = SimpleNamespace(field=.01, t_inter=-.1, **parameters['QAH'])

Doesn't make sense, since 'BHZ' and 'QAH' have most parameters shared.