Show address reuse warning

[dergigi]

Currently, it is not only possible to reuse addresses in Jam, there is also no indication that there's anything wrong with that. We probably want to, at the very least, show a warning. We should be able to easily do this for all "internal" Jam addresses, i.e. if you accidentally paste the same address twice (e.g. to fund a jar with multiple transactions).

It would also be good to show a warning in general, for any address, but we can't query the backend for that as of now.

We could also think of a "strict" setting that doesn't allow any reuse at all, no matter what.

[MaxHillebrand]

This warning should also be in the receive page.

Warning in the send tab only solves in-wallet self spends, but most cases are when sending from external wallets.

Hiding addresses that have received a coin might be an option.

[ghost]

This warning should also be in the receive page.

The receive page will only ever show you new addresses. We query the backend for a new address on every render of the page.

[ghost]

Agreed, we should to show a warning to prevent the address reuse from happening in the first place.

Just to bring it up here: If address reuse happens nonetheless, the backend will automatically freeze the second UTXO and label the address as reused.