Send avatar in vCard

[link2xt]

#1256

• Set FN and EMAIL fields
• base64-encode avatar blobfile into vCard
• Do not base64-encode vCard itself
• Parse avatars from vCard

[r10s]

the currently released versions would pass a vcard from Chat-User-Avatar directly to the ui, so we should be a bit careful about what we're sending out.

i think, we should roll out this in two steps:

• first, pushing a version that can accept jpg and vcard avatars but still sends out jpg
• a month later, with the next version, we can then send out a vcard

[r10s]

wondering if we shoud drop the Chat-Group-Avatar and Chat-User-Avatar headers and just use well-known filenames as for location-streaming. this could make things with outlook easier - less headers, less pain :)

by repeating the email-address resp. the group-id in the file, we can make sure, messages forwarded in normal MUA do not harm.

we could use a simple name as user.vcard (and maybe group.vcard if we want to target group-avatar handling in the same pr)

[hpk42]

@link2xt i suggest to retire this PR and convert it into an issue referencing the branch if useful.

[link2xt]

Thunderbird has an option "Prefers to receive messages formatted as:". When set to "Plain Text" (other options are "Unknown" and "HTML"), it adds x-mozilla-html:FALSE line to vCard. Makes sense to add this one for Delta Chat vCards too, Thunderbird uses this information to decide on the format when sending to users from address book.

[link2xt]

vcard crate creates vCards but does not parse them. Now need ical crate to parse them.

[link2xt]

Seems ical crate mimics ical.js and just the same does not parse vCard 2.1, which Thunderbird sends. Not a big deal as DC is going to generate vCard 4.0, but this hack from Thunderbird may be useful if we ever want to parse vCard 2.1: https://hg.mozilla.org/comm-central/file/4c8d82dc0948dd9aaedbc9e21f63ef5f8d96736c/mailnews/addrbook/modules/VCardUtils.jsm#l100

[link2xt]

Made a fix for ical crate: Peltoche/ical-rs#37

[r10s]

note: as discussed recently on another channel, before we continue working on this pr, we will check if maybe adding the image to the "body part header" might be the better option.

[link2xt]

This is replaced with #2232