This fixes missing translation tags in our missed-message emails,
which is surely the most user-facing part of the production that
wasn't internationalized.
Fixes: #14398
Making sender name go in-line with message body only if
the html starts with <p> tag since it won't look good
if the message starts with a code snippet, ul, etc.
If message starts with p tag we can safely assume that
it can go in-line with sender name.
This is a dramatic redesign of the look and feel of our missed-message
emails, designed to decrease the feeling of clutter and just provide
the content users care about in a clear, visible fashion.
This cleans up the reply_warning feature in favor of a more coherent
explanation of whether or not one can reply.
(Also, critically, it now advertises the ability to enable
missed-message email replies with some administrative configuration
work.)
We now include whether the message was a private or group private
message; this is particularly important with the new setting to
disable including any message content in these emails (since in that
case, one doesn't know anything about the message types).
Make sure 's, &s, and other characters are not HTML-escaped in subject
lines and plain-text emails.
Hack so that this isn't blocking the release of Zulip 1.6. A more robust way
to do this would be to have two different template Engines, one that renders
HTML, and one that doesn't.
Fixes#5088.