* Add confirmation step for email changes

This adds a confirmation step for email changes of existing users.
Like the initial account confirmation, a confirmation link is sent
to the new address.

Additionally, a notification is sent to the existing address when
the change is initiated. This message includes instruction to reset
the password immediately or to contact the instance admin if the
change was not initiated by the account owner.

Fixes #3871

* Add review fixes

* delete X-UA-Compatible

* undo

* restore

Serbian latin (sr-Latn) is generated automatically from Serbian (sr) translation. Also changed some wording in original (Serbian) translation.

* Adding Serbian translation

* i18n-tasks normalize

Relates to #6125, #6099

* Add GET /api/v1/instance/peers API to reveal known domains

* Add GET /api/v1/instance/activity API

* Make new APIs disableable, exclude private statuses from activity stats

* Fix code style issue

* Fix week timestamps

* Make host_meta/webfinger replies cacheable (fixes #6100)

Drop common code for handling users and sessions as webfinger queries
are very basic, public APIs.

Also explicitly mark results as cacheable with “expires_in”.

* Add “Vary: Accept” header for caching since content-negociation is used

Getting Started column obtained many links, and it became much taller.
Because of its height, Getting Started column required long scrolling on
devices with small screen, such as 4 inch phones and 10 inch laptops.

This change moves the mastodon which took large space on the column to
drawer column. The drawer column has only the compose form and has more
space.

* removed references to hideOnMobile in column_link and getting_started

* add mute, block, conversationMute actions to detailed status dropdown (fixes #1226)

* remove unused withDismiss in detailed status

* Add rake task to check and purge accounts that are missing in origin

* Add progress bar and --force options to mastodon:maintenance:purge_removed_accounts

* Add aria-autocomplete='list' in Textaria

ref: https://www.w3.org/TR/wai-aria-1.1/#aria-autocomplete

* Make detect empty string brefore assign upload description

* Change code elements in keyboard-shortcuts component to kbd

* Add validation for onMuteNotifications

* Reduce motion for boost animation

Fixes #5833

* Fix ternary expression

* Remove onSave method in mapped properties for column_settings

* Make web_push_subscription.register an action

* removed references to hideOnMobile in column_link and getting_started

* move keyboard shortcuts back below blocked users

* enforce https in production

* note changes in production env sample

* typo fix

Deleted users are technically suspended, but the code displaying their status
in the admin interface was broken and displayed a javascript object holding
translations of the possible user roles instead.

* Add aria-autocomplete='list' in Textaria

ref: https://www.w3.org/TR/wai-aria-1.1/#aria-autocomplete

* Make detect empty string brefore assign upload description

* Change code elements in keyboard-shortcuts component to kbd

* Update Korean translation

* Translate Korean for javascript

* Add missing translations on simple_form

* Add Slovak translation

* Slovak translation: i18n-normalize

2.1.0. -> 2.1.0