[Feature] Support for multiple wallets

[DanConwayDev]

I'd like to have two separate wallets or 'accounts' in Minibits so i can segregate funds without have to use a separate andriod profile, or different cashu app.

[minibits-cash]

Will think of proper way how to design this over the longer time horizont. Minibits is already multi-mint and multi-currency, co making it multi-wallet is not only technical but as well an UX challenge.