Add export / import app settings to file, for users without Google account

[FoxP]

Hello, Thanks for this amazing app. 👍

Idea / feature request :

If you don't have / want a Google account, there is no way to export / import app settings to / from a file. I learnt it the hard way, my phone randomly died some days ago.

Using the very latest version of Twire from F-Droid. Thanks, Best regard