enable BccSelf by default

[r10s]

enabling BccSelf improves user experience as
it is easier to set up another device
and ppl will also see "all" messages in other user agents directly.

for uncounted user problems, after diving into the issue,
the resulting device was "turn on BccSelf".
disabled BccSelf was probably the the number one single reason
of user problems.
(just recently again, this is the reason for this change, that, however, was discussed offline many times, but it never ends in a pr :)

main drawback of the change are potentially double notifications
when using a shared account and having another mail app on the same device (see #825).
however, we meanwhile do not recommend shared accounts at all,
the issue is also fixable by the other mail apps (as done by K-9)
and could be even regarded as a feature (you can decide which app to use for ansering).
but at the end the drawback is probably much smaller than the issues reported above.

@adbenitez if we want that change also for nauta, we also have to adapt nauta's provider-db entry.

[adbenitez]

agree that it is better enabling it by default, annoyances with contacts having issues with multidevice setup has become a more visible issue lately.

I think even for nauta it would be ok, because due to "delete messages from server at once" no copy to self is sent anyway IIRC, was it even disabled for nauta??? that is not necessary

[r10s]

I think even for nauta it would be ok, because due to "delete messages from server at once" no copy to self is sent anyway IIRC, was it even disabled for nauta??? that is not necessary

i double checked, indeed the bcc_self instruction is void if delete_server_after is set to 1 (converted to Some(0) here). so, for nauta, the default does not change.

[r10s]

i think, the clippy errors from https://github.com/deltachat/deltachat-core-rust/pull/3612/checks?check_run_id=8531158005 are unrelated? wondering, why ci on master is green then, cc @link2xt @flub

[link2xt]

i think, the clippy errors from https://github.com/deltachat/deltachat-core-rust/pull/3612/checks?check_run_id=8531158005 are unrelated? wondering, why ci on master is green then, cc @link2xt @flub

clippy runs on stable and Rust 1.64 with new clippy was just released. Maybe we should just pin clippy to 1.63 and update it from time to time together with fixing clippy bugs.

[link2xt]

1. What happens if user never changed this setting before? Looks like it will become enabled automatically, probably ok. But if user opened the settings window before, then UI probably saved "0" explicity and it will not be updated. We don't have explicit "default, user never touched this setting" value like e.g. about:config in firefox/thunderbird has, so there may be some difference in behaviour for different UIs.

2. There is still a maybe_add_bcc_self_device_msg which just became less useful, but seems worth keeping in case user disabled BCC to self explicitly.

[r10s]

ah, yes, forgot about that there is a maybe_add_bcc_self_device_msg :) but i agree, it is good to keep that, esp. as we reliably change the default only for new installations.