Improve docs

Add mix pleroma.user unsubscribe to mix doc

See merge request !512

Mix Tasks: Fix a typo in relay.ex moduledoc

See merge request !513

add common.ex

See merge request !511

Rebased !243

See merge request !509

Fix put_settings and remove info_changeset

See merge request !507

Correct and improve http options

See merge request !505

Add a MRF Policy for appending re: to identical subjects in replies.

See merge request pleroma/pleroma!499

Web Push Subscriptions

See merge request !506

# Conflicts:
#	lib/pleroma/application.ex
#	lib/pleroma/plugs/oauth_plug.ex

# Conflicts:
#	lib/mix/tasks/sample_config.eex
#	lib/pleroma/web/twitter_api/controllers/util_controller.ex
#	mix.exs
#	mix.lock

[#210] TwitterAPI: alt text support for uploaded images. Mastodon API uploads security fix.

See merge request !496

Refactoring.