Fixes #780

Fixes #778

Fixes #672

* Downcase signed_headers string before building the signed string

The HTTP Signatures draft does not mandate the “headers” field to be downcased,
but mandates the header field names to be downcased in the signed string, which
means that prior to this patch, Mastodon could fail to process signatures from
some compliant clients. It also means that it would not actually check the
Digest of non-compliant clients that wouldn't use a lowercased Digest field
name.

Thankfully, I don't know of any such client.

* Revert "Remove dead code (#8919)"

This reverts commit a00ce8c92c.

* Restore time window checking, change it to 12 hours

By checking the Date header, we can prevent replaying old vulnerable
signatures. The focus is to prevent replaying old vulnerable requests
from software that has been fixed in the meantime, so a somewhat long
window should be fine and accounts for timezone misconfiguration.

* Escape users' URLs when formatting them

Fixes possible HTML injection

* Escape all string interpolations in Formatter class

Slightly improve performance by reducing class allocations
from repeated Formatter#encode calls

* Fix code style issues

Fix #8685

* cleanup pass

* undo mistakes

* fixed.

* revert

SignatureVerification#matches_time_window? is not called anywhere.

* Add conversations API

* Add web UI for conversations

* Add test for conversations API

* Add tests for ConversationAccount

* Improve web UI

* Rename ConversationAccount to AccountConversation

* Remove conversations on block and mute

* Change last_status_id to be a denormalization of status_ids

* Add optimistic locking

Port 28401962ca to glitch-soc

Port 185cb2dc3a to glitch-soc

Media modals push an history state so that pressing back on mobile closes them.
We made sure to not scroll when opening them, but not when *closing* them,
which caused some issues in rare cases.

Signed-off-by: Marcin Mikołajczak <me@m4sk.in>

* Change documentation URL

* Fix hardcoded documentation URL in locales

* RTL: fix margins of public-account-header__tabs

* fix style

* even more stylish code :)

* Force use language detector if account is remote

* Set unknown remote toot's language as nil

* Add a confirmation dialog when hitting reply and the compose box isn't empty

Fixes #878

* Performance improvement

Configurable soft limit of 7,500, and above that, configurable
ratio of 1.1 * followers, controlled by:

- MAX_FOLLOWS_THRESHOLD
- MAX_FOLLOWS_RATIO

Fix #2311

Inspired by b79ab15859

Port f7a6f9489d to glitch-soc

[API] [vanilla required] [glitch-soc optional] initial_state show_sensitive_media boolean changed to show_media string with options "default", "hide_all", "show_all"

Port df2f4052b8 to glitch-soc

Port 9f6662fcc9 to glitch-soc

Port d0d65b5a28 to glitch-soc

Ruby's ** operator does not play well with non-Hash objects, which
the params slice is

Fix #8821

* RTL: fix margins: public-layout.header.nav-button

* add empty line to meet style guides