fix(finance-portal-ui/issues/55): fixed decimalRate configuration for displaying forex rate

fix(finance-portal-ui/issues/55): fixed decimalRate configuration for…

… displaying forex rate (#56)

* Fixed DecimalRate configuration for displaying forex rate & removed 644 report in FP

* Linted the code for the changes made

* Refactor logic using @mojaloop/ml-number library

* Added more tests for ForexRatesTab and added myself as a contributor

* updated comments for disabling 644 report

* fixed issue with stringRateFromDecimalRateAndInteger

- catered for 0 case
- also returned string with fixed decimateRate
- fixed unit tests

* Updated comment

* aligned import for consistency

Co-authored-by: Miguel de Barros <miguel@debarros.me>