Fix #7144

Port ba917e15f6 to glitch-soc

Port 74dae9458d and related to glitch-soc

Fix #7303

* Fix handling of malformed ActivityPub payloads when URIs are nil

* Gracefully handle JSON-LD canonicalization failures

Port the SCSS changes from cb74c0cfe4 to glitch-soc

Port SCSS changes from 5acd5315f2 to glitch-soc

Port 8c601b54cc to glitch-soc

Port 58852695c8 to glitch-soc

* Prevent Enter keypresses from triggering dropdown display toggle twice
* Give focus to first/selected item of dropdown menus
* Implement keyboard navigation in generic dropdown menus

Partial port from ef7d64c801 to glitch-soc

Port ad5d3134e4 to glitch-soc

Fix #7335

* Store home feeds for 7 days instead of 14

Reduces workload for status fan-out to active followers

* Fix test for user model

* Mark currently selected privacy setting in privacy dropdown

* Prevent Enter keypresses from triggering dropdown display toggle twice

* Give focus to first/selected item of dropdown menus

* Implement keyboard navigation in privacy dropdown

* Implement keyboard navigation in generic dropdown menus

Conflicts:
 	app/controllers/follower_accounts_controller.rb
 	app/controllers/following_accounts_controller.rb
    	db/schema.rb

Same URI passed between follow request and follow, since they are
the same thing in ActivityPub. Local URIs are generated during
creation using UUIDs and are passed to serializers.

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

Conflicts:
 	CONTRIBUTING.md

“Enable” high contrast theme

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

Conflicts:
 	Gemfile.lock

Fix #6994

[Glitch] Improve relative timestamps in web UI

Well, it seems unnecessary, anyway.

Conflicts:
 	.travis.yml
 	Gemfile.lock
 	README.md
 	app/controllers/settings/follower_domains_controller.rb
 	app/controllers/statuses_controller.rb
 	app/javascript/mastodon/locales/ja.json
 	app/lib/feed_manager.rb
 	app/models/media_attachment.rb
 	app/models/mute.rb
 	app/models/status.rb
 	app/services/mute_service.rb
 	app/views/home/index.html.haml
 	app/views/stream_entries/_simple_status.html.haml
 	config/locales/ca.yml
 	config/locales/en.yml
 	config/locales/es.yml
 	config/locales/fr.yml
 	config/locales/nl.yml
 	config/locales/pl.yml
 	config/locales/pt-BR.yml
 	config/themes.yml

* Revert "Fixes/do not override timestamps (#7331)"

This reverts commit 581a5c9d29.

* Document Snowflake ID corner-case a bit more

Snowflake IDs are used for two purposes: making object identifiers harder to
guess and ensuring they are in chronological order. For this reason, they
are based on the `created_at` attribute of the object.

Unfortunately, inserting items with older snowflakes IDs will break the
assumption of consumers of the paging APIs that new items will always have
a greater identifier than the last seen one.

* Add `override_timestamps` virtual attribute to not correlate snowflake ID with created_at

The previous rate limit allowed to post media so fast that it is possible
to fill up the disk space even before an administrator notices. The new
rate limit is configured so that it takes 24 hours to eat 10 gigabytes:
10 * 1024 / 8 / (24 * 60 / 30) = 27 (which rounded to 30)

The period is set long so that it does not prevent from attaching several
media to one post, which would happen in a short period. For example,
if the period is 5 minutes, the rate limit would be:
10 * 1024 / 8 / (24 * 60 / 5) = 4

This long period allows to lift the limit up.