v3 improvements: representation on balances in GUI

[evd0kim]

User suggested to remove sats balance and demonstrate fiat balances only. I'd agree.

Here I propose for main window cards:

• [ ] disable bitcoin card when balance is 0 (add setting "Always show bitcoin balance card")
• [ ] make sats balances optional (add setting "Always show sats balance on LN card")

Disabling Bitcoin balances card may free some space for other useful features.