small improvements to backup transfer progress dialog

[Simon-Laux]

• while progress == 0 show some message like "establishing connection between devices", hide the message as soon as there's progress or replace it with a new message that says "transferring"

• set a timeout of one second, if there is no progress until then show a link/button to troubleshooting steps.

The second point is actually the more important one -> if the user likely has trouble point them to FAQ, where they can get help.

[iequidoo]

• while progress == 0 show some message like "establishing connection between devices", hide the message as soon as there's progress or replace it with a new message that says "transferring"

Made a small improvement so that "transferring" may be displayed earlier on the receiver side: deltachat/deltachat-core-rust#6347