Fix #11270

* Fix BackupService crashing when an attachment is missing

For various reasons such as admin error or out-of-sync media and
database backups, it might be possible for local attachments to be lost.

This commit allows the BackupService to continue its work even if some media
file is missing.

* Change error message

* Disable incorrect check for hidden services in Socket

Hidden services can only be accessed with an HTTP proxy, in which
case the host seen by the Socket class will be the proxy, not the
target host.

Hidden services are already filtered in `Request#initialize`.

* Use our Socket class to connect to HTTP proxies

Avoid the timeout logic being bypassed

* Add support for IP addresses in Request::Socket

* Refactor a bit, no need to keep the DNS resolver around

* Remove Salmon and PubSubHubbub endpoints

* Add error when trying to follow OStatus accounts

* Fix new accounts not being created in ResolveAccountService

Avoids jumping the scroll around vertically when giving it focus and
editing long toots.

Use the smallest preset expires_in such that the new poll would
not expire before the old one.

In the typical case of a quick delete & redraft, this results in
using the same poll duration.

Fixes #10567

* Add request pool to improve delivery performance

Fix #7909

* Ensure connection is closed when exception interrupts execution

* Remove Timeout#timeout from socket connection

* Fix infinite retrial loop on HTTP::ConnectionError

* Close sockets on failure, reduce idle time to 90 seconds

* Add MAX_REQUEST_POOL_SIZE option to limit concurrent connections to the same server

* Use a shared pool size, 512 by default, to stay below open file limit

* Add some tests

* Add more tests

* Reduce MAX_IDLE_TIME from 90 to 30 seconds, reap every 30 seconds

* Use a shared pool that returns preferred connection but re-purposes other ones when needed

* Fix wrong connection being returned on subsequent calls within the same thread

* Reduce mutex calls on flushes from 2 to 1 and add test for reaping

When editing a custom filter, select the shortest preset duration that
still covers the remaining time of that filter.

Fixes #9506

Resolve #11187

* Optimize makeGetStatus

Because `ImmutableList.filter` always returns a new object and `createSelector`
memoizes based on object identity, the selector returned by `makeGetStatus`
would *always* execute.

To avoid that, we wrap `getFilters` into a new memoizer that memoizes based on
deep equality, thus returning the same object as long as the filters haven't
changed, allowing the memoization of `makeGetStatus` to work.

Furthermore, we memoize the compiled regexs instead of recomputing them each
time the selector is called.

* Fix memoized result being cleared too often

* Make notifications use memoized getFiltersRegex

In some occasions, such as the browser or a browser extension auto-filling
the existing but disabled/hidden CW field, a CW can be set without the user
knowing.

Follow-up to #11112

Fix #7940

Fixes #9779

* Add message telling FTS is disabled when no toot can be found because of this

Fixes #11082

* Remove info icon and reword message

* Fix account URI in UpdatePollSerializer

Fixes #11185

* Add specs

* Add option to disable blurhash previews

* Update option text

* Change options order

Fixes #11127

* Apply filters to poll options in WebUI

Fixes #11128

* Apply filters to poll options server-side

* Add poll options to searchable text