Use Jason for rendering responses

See merge request pleroma/pleroma!1655

Although Jason readme says Phoenix 1.4+ already does it by default, [it actually does it only for new projects](https://github.com/phoenixframework/phoenix/blob/3bfb9f6e900c9a2e31cb95736e2cb5bdad329b61/lib/phoenix.ex#L58-L59)

Mastodon API: URI encode hashtag name in generated URLs

See merge request pleroma/pleroma!1642

Revert "Parallelize template rendering"

See merge request pleroma/pleroma!1654

This reverts commit 1ad71592.

Since it had no limit on the number on concurrent processes it OOM killed
instances while rendering hellthreads. When I tried introducing a
concurrency limit with Task.async_stream/manual folds it lead to about 3 times
worse performance on threads larger than 1000 activities (we are talking
30s vs 1.2 minutes), I think this is not worth the about 1.5 times
performance increase on smaller threads when using it.

Fix tests for `Activity.all_by_ids_with_object/1`

See merge request pleroma/pleroma!1652

Add an endpoint to get multiple statuses by IDs

Closes #1240

See merge request pleroma/pleroma!1621

Add Pleroma.Plugs.Cache

Closes #1174

See merge request !1612

Update CHANGELOG (add a note about !1649)

See merge request !1650

Fix `ActivityPubController.read_inbox/2`

Closes #1248

See merge request pleroma/pleroma!1649

Otherwise hashtags with word characters other than those allowed in URLs (e.g. Japanese characters) produce hashtag URLs that are invalid.

chore: query optimization

Closes #1224

See merge request pleroma/pleroma!1640

the PostgreSQL query planner is easily confused due to the complexity of
certain queries we make.  while we plan to simplify these queries through
unification of activities and objects, we are not yet there.  it has been
discovered that using a precalculated list of deactivated users encourages
the query planner to prefer simpler indices instead of the
activity_visibility index.

accordingly, drop the subquery and precalc the user list instead.

using an indexed value in thread_mute table helps ecto build a better query.

Prioritize the removal of TwitterAPI and :accept_blocks in the changelog

See merge request !1638

Removing TwitterAPI

See merge request !1605

Update frontend bundle to e75ac9dd

See merge request !1635

Call TrailingFormatPlug for /api/pleroma/emoji

See merge request !1634

Apparently Pleroma-FE still calls it with trailing '.json'

Mastdon API: Add ability to get a remote account by nickname to `/api/v1/accounts/:id`

See merge request !1622

Mastodon API Poll view: Fix handling of polls without an end date

See merge request !1631

Do not crash if one notification failed to render

See merge request !1630

Update Dockerfile + some touchups to docker.exs

See merge request pleroma/pleroma!1624