cms.utils.plugins builtins refactors

requires_reload(): any()
downcast_plugins(): list comp
cms.utils.django_load iterator refactors, using Py3-like builtins

iterload(): filter()
iterload_objects(): map()
cms.utils.i18n: builtins refactors

get_language_list, get_language_tuple, get_public_languages: list comps
get_language_dict: dict(get_language_tuple)
is_language_prefix_patterns_used: any()