[Pleroma.Web.TwitterAPI.UserView]: Add mastodon-fields in "fields"

See merge request pleroma/pleroma!360

activitypub: don't fall back to OStatus fetching when MRF rejects an object

See merge request !362

activitypub inbox: only accept unsigned/invalid-signature relayed creates, nothing else

See merge request !361

although the previous handling assumed any unsigned/invalid signature message was a Create,
lets make it more explicit

More kroeg bugfixes

See merge request !353

Also simplified the code for name trimming.

And not copying the Map.merge part as it looks buggy.
See: https://queer.hacktivis.me/objects/a9f21ebc-9a12-4a6c-89d5-3d46955c6ee8

Uploaders.S3: Replace unsafe characters in object key

See merge request pleroma/pleroma!359

According to [the S3 docs][s3], the characters safe for use in object keys are:

* 0-9
* a-z
* A-Z
* !
* -
* _
* .
* *
* '
* (
* )

(The / character is not listed but mentioned being safe outside of the list.)

Several characters that are valid in filenames can cause problems, for example
spaces are not valid in URLs and need to be escaped,
sequences of spaces can become squeezed by S3,
some characters like \ are documented to require “significant special handling”.

To avoid these problems, this change encodes the filename
before using it as part of the S3 object name
by replacing all characters except those documented as “safe” with dashes.

[s3]: https://docs.aws.amazon.com/AmazonS3/latest/dev/UsingMetadata.html

update pleroma frontend

See merge request pleroma/pleroma!357

html: add scrub policy tests

See merge request pleroma/pleroma!356

twitter api: add no_rich_text option to userview for account prefs

See merge request pleroma/pleroma!355

backend support for opting out of rich text on a per-account basis

See merge request pleroma/pleroma!354