This introduces a state machine which takes care of managing the
handshake transitions in the secure-join protocol. This separates
user interactions from the protocol state handling.
This means that while handling the protocol state there are a bunch of
failures no longer possible due to all state information being
guaranteed to be present. As part of this the QR-code state has been
extracted from the generic Lot structure to something suitable just
for the SecureJoin protocol.
A LogSink has been added to the testing tools allowing log messages to
be correctly displayed on test failures.
This also checks that some of the correct user interactions happen,
checking we get a joiner event and the verified chat messages.
It also extends the test utils with the ability to distinguish the
different context logs by having them named.
'Delete emails from server' was an experimental ad-hoc function
that was added before 'Automatically delete old messages' was introduced
to allow at least some way to cleanup.
'Delete emails from server'-UI was already removed from android/ios in june
(see https://github.com/deltachat/deltachat-android/pull/1406)
and the function never exists on desktop at all.
Since stock string callback has been deprecated, all event callbacks
return 0.
For compatibility, C declarations are not changed and FFI users are
expected to return 0 from their callbacks.
This more strongly types the ubiquitous message id type by no longer
making it an integer. It keeps the actual ID opaque. Only for the
generic job API the number keeps being used. Some locations also need
to create it from an integer and call MsgId::new().
