[Enhancement] Add in-app QR-code scanner

[schlagmichdoch]

This issue was deleted by GitHub (via hubot) as part of mistakenly marking this account as spam on 17th February 2024. The creation date is unclear. There are also links to the deleted issue that are not updated to this issue. I decided to manually recreate it anyway in order to complete the information the repo holds even though the restored information might be outdated:

Issue by @schlagmichdoch:

As discussed in #254, if PWAs are in standalone mode they cannot scan the QR codes anymore.

„There could also be the possibility to add a QR code scanner to PairDrop itself. This would make it possible to use QR codes from inside the PWA or an app (like Snapdrop & PairDrop for Android).“

Originally posted by @schlagmichdoch in #254 (comment)

Current idea:
To activate it, add a camera button to the top left corner.
Only show the button if display is standalone and device is Android / iOS.

In order not to clutter the header bar, it should be rearranged: the edit paired devices icon should be hidden. Clicking/hovering over the pairing icon should expand it downwards like so:
(A) (B) (C) (D)
-click on B->
(A) (C) (D)
(E) (F)

B: current Pair icon
E: current Edit Paired Devices icon
F: current Pair icon with small plus next to it