* let sending invalid webxdc fail
invalid webxdc can still be send as Viewtype::File, however
(maybe one want to discuss errors or so ;)
* clarify the supported zip compression methods
* add a test for unencrypted replies to encrypted webxdc instances
* make update messages work if a key is missing
even in opportunistic chats,
replies to encrypted messages are forced to be encrypted,
if that is not possbile, message sending fails.
while this is okay to not leak previously send text messages,
the quotes as used by webxdc are more artificial,
currently only the static text "Webxdc".
* changelog ...
* fix forwarding webxdc instances, add a test for that
* adapt webxdc test to fail on info-messages added when in draft mode
* do not add info-messages when in draft-mode
* half the number of instance-loads per webxdc update send/receive
the summary can be modified by the apps using
`sendUpdate({summary: "foo", payload: ...})`
the summary is updated when there is no newer update
and chat will be informed by the change as usual by
`DC_EVENT_MSGS_CHANGED`.
additional parameters will be `summary` and `msg` (for an info-message)
right now, and maybe more in the future (`aggregated`, `fast`, `to` ...),
so adding just more parameters easily gets wild.
also, this makes adaptions easier as no ffi needs to be adapted
when we add more parameters.
finally, sending is in-sync with receiving, database and wire now,
one receives similar objects as one sends,
which also looks like the right thing :)
for now, `sendUpdate()` also allows to use the old, unwrapped payload
to not immediately break existing `.xdc`, however, that will be removed soon,
probably before the first release.
