Rethink the currencyFormatter's implementation

[nortonandreev]

Follow the discussion here.

Essentially, we should think of:

• Extracting the minimumFractionDigits value and replacing the hardcoded values with constants
• Splitting the generic currency formatter and the DUSK formatter into two separate modules

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[kieranhall]

It's probably a good idea to separate formatting of currencies based on if the currency is a crypto-currency or a fiat-currency.

[ascartabelli]

This should be solved by tackling dusk-network/rusk#1314, but keeping it open in the meanwhile.