Add PUT /api/pleroma/notification_settings endpoint

docs/Pleroma-API.md

lib/pleroma/notification.ex

lib/pleroma/user.ex

lib/pleroma/user/info.ex

lib/pleroma/web/mastodon_api/views/account_view.ex

lib/pleroma/web/router.ex

lib/pleroma/web/twitter_api/controllers/util_controller.ex

test/web/mastodon_api/account_view_test.exs

test/web/twitter_api/util_controller_test.exs