add-second-device strings missing

[r10s]

the idea of the "Add as Second Device" button in the "Welcome" screen is to let ppl not run into problems when setting up a second device.

while the general functionality is there and working nicely, a hint is missing what ppl should do. currently the screen looks like the following:

unless ppl have read instructions somewhere else, they are left completely alone.

as a minimum, we should replace the title and the text below the qr code with multidevice_receiver_title resp. multidevice_open_settings_on_other_device. ftr, is how android/ios look:

related: in the subsequent progress dialog, the title string is missing:

that should be multidevice_receiver_title as well.

[r10s]

i assume, the refactoring milestone is not a prerequisite for changing strings?

i'd change these strings as soon as possible, not a blocker and maybe not the reason for a 1.36.1+, but still should be part of it when it is needed because of other things.

to be clear: no need to change the whole layout now to match android/ios, just change the hint is already a huuuuge ux improvement (also ios was only about getting some hints in, without much effort - but does not look that bad at the end :)

[Simon-Laux]

the problem is the qr code scanner (which is inside of a dialog), we would need a custom ui there and if we're already doing that then we can do the new scanner as well, it's not that hard.