Added currency option feature

[SurajNarang]

Added currency option feature for improved user experience and clarity

[YahiaElTai]

Hey @SurajNarang Thanks so much for submitting the PR. The change is indeed very useful, few notes from me before merging.

1. It would be great to add a screenshot of the UI change when you submit a PR with UI changes (saves the reviewer some time)
2. I would also be great if you could keep all the JS within the js file and not in index.html
3. The design of the currency selector is a bit off from the design of the app, It would be great to add some CSS to it to make it look nice.
4. The currency selector I think would look better if it was somewhere around where the balance is shown
5. Just an idea: It would be nice if the currency was displayed with the balance

Hope you can find these comments helpful and thank you for the PR :)