general backend cleanup

Created by: zeffii

This PR will include miscellaneous modifications to increase test readability. Have patience.

• filename from search_enum produces awkward data.

• at the end of a sverchok session, there's a massive printout of the exception.

def sv_unregister_modules(modules):
    clear_system_cache()
    for m in reversed(modules):
        if hasattr(m, "unregister"):
            # print("Unregistering module: {}".format(m.__name__))
            if m.__name__ == "sverchok.old_nodes":
                import bpy
                old_node_names = sverchok.old_nodes.old_bl_idnames
                loaded = any([hasattr(bpy.types, node_class_name) for node_class_name in old_node_names.keys()])
                if not loaded:
                    print("skipping unregister of old nodes..they are not registered")
                    continue
            try:
                m.unregister()
            except RuntimeError as e:
                print("Error unregistering module: {}".format(m.__name__))
                print(str(e))