The automated message when setuping multiple devices isn't accurate

[narFnarF]

The automated message that appear when setuping multiple devices isn't accurate.

The current message:
It seems you are using multiple devices with Delta Chat. Great!
If you also want to synchronize outgoing messages accross all devices, go to the settings and enable "Send copy to self".

Multiple issues with this message:

1. The instruction are vague: There's no "Send copy to self" option in Settings. We need to navigate to the Advanced menu.
   • Solution: Rephrase the last sentence. "go to Settings, then Advanced and enable "Send copy to self". "
2. The setting of sending a copy to self is currently already ON by default. Maybe this whole message is unecessary?
   • Solution: Detect if the setting is already turned ON and avoid displaying these instructions
3. Typo in "accross". Should be "across".

[Simon-Laux]

Transferred the issue to the core repo string is here:

deltachat-core-rust/src/imex.rs

Lines 250 to 254 in 45462fb

	msg.text = Some(
	"It seems you are using multiple devices with Delta Chat. Great!\n\n\
	If you also want to synchronize outgoing messages accross all devices, \
	go to the settings and enable \"Send copy to self\"."
	.to_string(),

[gerryfrancis]

To add: Messages sent in the past but not to self are not synchronized, I think this should be mentioned in the notes, too.

[Septias]

1. I think it's hard to unify the instructions to enable send copy to self because every UI can have a different settings menu. But @Hocuri, @r10s and @Simon-Laux know more about this I guess. If alle the UI's are similar in this regard, we could change the wording.

2. This line should prevent any user that has bcc-self (send message to self) activated to received said message and in fact for me it didn't show up with this workflow:

   1. Create acc on phone & create Backup
   2. Load backup on desktop

Maybe you can recheck or tell me what you did exactly?

[Hocuri]

One problem can't be reproduced, the other one is reeeally easy to fix, I'll do a PR.

@Septias Thanks for digging up this old low-hanging fruit and pining me.