Since try_decrypt does not check if the message has valid signatures
anymore, it may return empty signatures set, which means the message is
not a valid autocrypt message.
this pr allows prefixing custom jitsi urls with `jitsi:`
so that clients have a chance to detect these custom instances
and may start the corresponding app.
introduce the qr-code-type `DCWEBRTC:[webrtc_instance]`.
dc_check_qr() returns this as the type DC_QR_WEBRTC
and these qr-codes can be passed to dc_set_config_from_qr() then;
this finally sets `webrtc_instance` using dc_set_config().
needed for how node/js handles the chatlist currently
(it convertes the ffi-object to an js-object and throws ffi-object away directly,
this makes it hard to access dc_chatlist_get_summary() later.
Since introduction of provider database, these certificate checks are
enabled for test servers anyway, but this setting prevents usage of
local servers with self-signed certificates.
It presents no security issue, because properly configured servers will
only serve passwords on HTTPS and distribute only HTTPS QR codes, but
makes testing easier when HTTPS is not easy to deploy.
If attacker can control the URL used, they can change the URL to another
HTTPS URL controlled by them and act as a proxy between the client and
original server anyway.
Adhoc groups for group messages that don't have Chat-Group-ID are already
created above in another create_or_lookup_adhoc_group.
At this point it could be that there is a valid Chat-Group-ID header,
but no group was created because removed_id was non-zero i.e. received
message removes some group member.
If group was not explicitly left, current code creates an adhoc group
instead of trashing late or reordered messages that remove group
members. Such groups have adhoc group IDs locally, but proper group
message-IDs. Attempts to reply to such groups or leave them creates
"split groups" for all other members of original group. The solution is
not to create adhoc groups in this case.
