util/index: convert js to ts

The languageModel & fiatModel interface created to type-check
the data and ensure that it conforms to
the expected structure and format.
This can help you avoid errors and bugs when
working with the data in your code.
This commit enables resolveJsonModule to import module
with '.json' extension.

tsconfig.json

@@ -1,6 +1,7 @@
 {
   "compilerOptions": {
     "strict": true,
-    "esModuleInterop": true
+    "esModuleInterop": true,
+    "resolveJsonModule": true
   }
 }

util/fiatModel.ts

@@ -10,3 +10,7 @@ export interface IFiat {
     price?: boolean;
     locale?: string;
 }
+
+export interface IFiatCurrencies {
+    [key: string]: IFiat;
+}