fix missing braces error for gcc-8

removed the last backward compatibility tests I missed the first time around.

missed some stuff in tests

cut all backwards compatibility changes from the patch, this is a pure prefix change now.

Cashtab does not have unit tests for these validation functions, will create some to support this change.

The figure 0.00000546 is the dust limit of the bch-api backend. If the app attempts to broadcast a transaction sending less then 0.00000546 BCHA, an error will be returned from the API. These hard coded 546-sat figures will be replaced by currency.ticker once the app sending limit is brought in line with the backend limit in a future diff.

This diff is actually doing several things at a time. Splitting it into pieces and stack them will make the review easier and will help getting this landed faster.

Rebase

Back to your queue due to test failures.

Remove debug logging

Add unit test for dust limit, add catch for dust to sendBCH function as dust error comes from server, implement BigNumber for dust constant

The test plan would benefit from being a unit test

discussed off Phab, the wait_until import should be removed in PR19752

put a comment on its own line