fa84723e73 amount: Move CAmount CENT to unit test header (MarcoFalke)
Pull request description:
`CAmount` is currently not type-safe. Exporting a constant (`CENT`) that is commonly not referred to by that name might be confusing. `CENT` is only used in two places prior to this commit (`ParseMoney` and `MIN_CHANGE`). So replace these with constants relative to `COIN` and move `CENT` to the unit test header.
Backport of Core PR14244