track fiat value of payments (#1789)

* save fiat_amounts on payment creation

* show fiat amount in frontend

* add lnbits_default_accounting_currency

* extract fiat calculation logic into service

* move all currency conversions to calc_fiat_amounts

move all conversion logic into create_invoice so extensions can benefit aswell

* show user-defined and wallet-defined currency in frontend

* remove sat from fiat units

* make bundle

* improve tests

* debug log

lnbits/static/i18n/en.js

@@ -29,6 +29,9 @@ window.localisation.en = {
     'This whole wallet will be deleted, the funds will be UNRECOVERABLE.',
   rename_wallet: 'Rename wallet',
   update_name: 'Update name',
+  fiat_tracking: 'Fiat tracking',
+  currency: 'Currency',
+  update_currency: 'Update currency',
   press_to_claim: 'Press to claim bitcoin',
   donate: 'Donate',
   view_github: 'View on GitHub',