if CommonAPI ever prevents us from injecting this data

Basic new user registration email, various improvements

See merge request pleroma/pleroma!3304

This reverts commit 5df9f68392.

MRF NoEmptyPolicy: Deny posts from local users if there is no content or only mentions.

See merge request pleroma/pleroma!3309

Helps prevent accidental button mashes from submitting incomplete posts

RSS: Make sure post URL is the first `<link>` element

See merge request pleroma/pleroma!3308

Otherwise some RSS readers (tested in Miniflux) might pick the context
URL as the external link.

Related to #2425.

More descriptions improvements

See merge request pleroma/pleroma!3307

Improve Mailer descriptions for AdminFE

See merge request pleroma/pleroma!3306

# Conflicts:
#   CHANGELOG.md

Suppress report notification for admin actors

See merge request pleroma/pleroma!3301

Add various labels, descriptions and suggestions for all adapter settings and try to use
the same terminology by the service provider.

This setting defaults to false so the relay host will be used in an MX query so
multiple SMTP servers can be used. gen_smtp code states that all records returned from the
MX query are attempted in order and only a permanent SMTP error will stop the client from
attempting other servers in the list. Connection failures, TLS issues, etc will cause it to
try the next host.

If there is no MX record associated with the relay host, it automatically tries connecting to it
directly.

There is really no reason to expose this to end users. The default value is fine for everyone.

allow user defined text search config in database

See merge request pleroma/pleroma!3275

Improve Varnish VCL

See merge request pleroma/pleroma!3305

This fixes connection failures when trying to retrieve large files.
It is less common in typical Pleroma usage, but it's possible to encounter
this on a cloud instance with lower memory.

Also only check for subject as the body is a mess of html and we don't really need to prove its contents if the subject matches.