[Cashtab] Additional mitigation for legacy wallet addresses

Summary: As noted in D15079, every now and again during testing where, for an old wallet, the address is stored with bitcoincash: prefix. This diff checks for all three derivations upon wallet load on startup in useWallet and convert to eCash prefix if needed.

Test Plan:

• npm test
• npm start
• Open a wallet and manually simulate this edge case where the wallet.Path1899.cashAddress value contains a bitcoincash: prefixed address. The easiest way to achieve this is to temporarily add:

const { type, hash } = cashaddr.decode(wallet.Path1899.cashAddress);
wallet.Path1899.cashAddress = cashaddr.encode('bitcoincash', type, hash);

near the top of isLegacyMigrationRequired along with debug logs right.

• Re-load cashtab then ensure debug logs reflect the detection of a non-eCash prefixed address for Path1899 and subsequent conversion to eCash prefix.
• Repeat for the Path245 and Path145 derivation path cash addresses.

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D15084