[Feature request] Add ability to export private key

[Jan-NiklasB]

Hey,
first at all, great app, often thought of something like this myself, but I'm lacking the knowledge in app dev.

Now to the request:
Could you implement the ability to export the private key, so one can backup it and also use it on multiple devices / profiles?

For example:
I'm using a private and business account on my phone for privacy reasons, so I have to install the app twice wo use it in both environments, but I can't sync the key between them, neither can I backup the keys.

Would be great, and I guess not that hard to implement.