[Cashtab] Patch bug in fee calculation for token creation

Summary: Bug in how transaction fees are calculated in token creation previously concealed by the high default app fee of 5 sat/byte. Reducing the fee caused token creation txs to fail. Investigating, bug in how default fee applied (should be in base units i.e. sats).

Test Plan:
npm test; note unit test has new mock raw hex as previous tx, while valid, did not correspond to app fee setting.
npm start
Create a token

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9586