Investigate SeedXOR support

[AndreasGassmann]

Coldcard released a new feature yesterday: https://seedxor.com

It's basically a simple and less powerful alternative to Shamir's.

The way it works is very simple, so integrating it would not be hard. But because it's a new standard, we will have to wait and see how the community reacts to it and if it becomes a new standard.

Some thoughts on using XOR for seeds: https://github.com/mmgen/mmgen/wiki/XOR-Seed-Splitting:-Theory-and-Practice