closes #7547

closes #7545

closes #7542

Fixes #7541

This commit introduces support for AccountMigration federation message
receive. It covers the cases when the new home pod for a user is remote
respective to the recepient pod of the message. It also allows to initiate
migration locally by a podmin from the rails console. This will give the
pods a possibility to understand the account migration event on the
federation level and thus future version which will implement migration
will be backward compatible with the pods starting from this commit.

updates tag to follow standard styleguide

This doesn't add any value in the post preview:
* Avatar is already at the left-hand side of the publisher
* Timestamp is always "less than a minute ago"
* Interactions are disabled in the preview anyway

We don't display these things in the comment preview either, they only
need space and don't add any value to the preview.

Otherwise the export stays soft-locked and the podmin needs to reset it
manually.

Fixes #6225

Also remove `disconnect_contacts` methods, because contacts are already
removed with aspects memberships in `before_destroy`.

The change in assets.rb should be enough, but it doesn't work, because
sprockets `after_initialize` runs before it and initializes sprockets
with unfiltered paths.

But the trick with the underscore works, because bootstrap-sass has
named the file `_bootstrap.scss`, and rails-assets-bootstrap has
`bootstrap.scss`, so with `_bootstrap` it uses the correct bootstrap.

Validation fails because there is no user set.

Return in scope fails with `LocalJumpError: unexpected return`

Also remove some unused html responses

ActionController::Parameters no longer inherits from HashWithIndifferentAccess

There were validation errors because `answer.poll` wasn't set.