Fix 4152: Currency as object

[Akarshit]

Resolves #4152
Impact: major
Type: bugfix

Issue

1. The findCurrecny function was returning shop.currency when it was unable to find the user's currency. But that function is supposed to return an object of type Currency.
2. While animating the background of input, a undefined value was being passed. This was happening because ref prop was not being set on the input inside NumericInput component.

Solution

1. Made the function to return shop.currencies[shop.currency], which is the actual value expected.
2. Passed ref=input to NumericInput.

Breaking changes

None

Testing

1. Reset reaction
2. Login as admin
3. Create a product
4. Click on the first variant so that the variant/option panel opens
5. Observe no error in console
6. After updating the price, observe no error about undefined promise.

[zenweasel]

Tested. Verified fixed