Facebook removed the API and facebook integration is broken now, so lets
remove it.

closes #7874

closes #7705

Fixes #5727

closes #7624

fixes #1649

closes #7629

Introduce Workers::Mail::NotifierBase to be a base for all appropriate
mail workers to reduce code duplication

closes #7223

closes #7158

closes #7050

Fixes #5116

and delete old batch worker and receiver

* add port to pods
* remove url from person and link people with pod-table

add tooltips in the frontend
fix a JS problem with empty hostname
use `find_in_batches` correctly
add a migration to clean up the pods table + unique index on hostname

* add a class for checking pod connectivity
* extend pod model to handle new functionality
* add an admin frontend to list pods and re-trigger checks manually
* add a daily worker to run through all the pods
* add unit tests for most of the new code

* .well-known/social-relay - to serve subscription preferences to relays
* Workers.deferred_dispatch relay carbon copy functionality for outbound sending

See discussion here: https://www.loomio.org/d/9vpoe0UR/public-post-federation#comment-730911 and spec here: https://wiki.diasporafoundation.org/Relay_servers_for_public_posts

closes #6168

closes #5983

closes #5960

It seems ActiveRecord ignores .limit() if .find_each() is used to iterate the query (http://stackoverflow.com/a/6680541/1489738). Using .each() instead. Added a test.

closes #5953

Fixes #5834