Need a way to exclude PayPal from orders with unsupported currencies

adding related issue, https://www.drupal.org/node/2860111

This was a setting previously which was missed in the port.

i'm not sure this feature it's needed.
imho: i translate this feature as multicurrency system that it doesn't really exists.
Of course it exists in the PayPal, but nothing to do with Commerce payment gateway here.

However i think there should be done more about supported currencies.

Maybe:
1. Do not add or save a Payment gateway is there is no supported currency in the system.
Maybe add the link to import currencies and display which currencies are supported

2. Do not use a Paypal Payment gateway in the checkout if the order does not have a PayPal supported currency.

@vasike for the same point(2) you said, i have raised an issue, which bojanz also agreed would be a feature request. see this: https://www.drupal.org/node/2860111

i'm writing a condition plugin using new condition API for commerce_currency entity. Will put a patch shortly at this issue: https://www.drupal.org/node/2860111

i have put a patch at related issue above which solves this as well.

Retitling for clarity.

Discussed this with jsacksick, we agreed that the right solution for this is to add sumanth's OrderCurrency condition to Commerce.

Committed the Commerce condition.