Merge branch '534_federation_targets_reachability' into 'develop'

config/config.exs

docs/config.md

lib/pleroma/instances.ex

lib/pleroma/instances/instance.ex

lib/pleroma/web/activity_pub/activity_pub.ex

lib/pleroma/web/activity_pub/activity_pub_controller.ex

lib/pleroma/web/federator/federator.ex

lib/pleroma/web/ostatus/ostatus.ex

lib/pleroma/web/ostatus/ostatus_controller.ex

lib/pleroma/web/salmon/salmon.ex

lib/pleroma/web/websub/websub.ex

lib/pleroma/web/websub/websub_controller.ex

priv/repo/migrations/20190123125546_create_instances.exs

test/support/factory.ex

test/support/http_request_mock.ex

test/web/activity_pub/activity_pub_controller_test.exs

test/web/activity_pub/activity_pub_test.exs

test/web/federator_test.exs

test/web/instances/instance_test.exs

test/web/instances/instances_test.exs