Refactor code to comply with credo suggestions

.credo.exs

lib/pleroma/plugs/authentication_plug.ex

lib/pleroma/upload.ex

lib/pleroma/user.ex

lib/pleroma/web/activity_pub/activity_pub.ex

lib/pleroma/web/ostatus/activity_representer.ex

lib/pleroma/web/ostatus/feed_representer.ex

lib/pleroma/web/ostatus/ostatus_controller.ex

lib/pleroma/web/ostatus/user_representer.ex

lib/pleroma/web/router.ex

lib/pleroma/web/salmon/salmon.ex

...roma/web/twitter_api/representers/activity_representer.ex

lib/pleroma/web/twitter_api/twitter_api.ex

lib/pleroma/web/twitter_api/twitter_api_controller.ex

lib/pleroma/web/web.ex

lib/pleroma/web/web_finger/web_finger.ex

lib/pleroma/web/web_finger/web_finger_controller.ex

lib/pleroma/web/websub/websub.ex

lib/xml_builder.ex

mix.exs