continuation of PR #8161 Display error notification when attempting to purchase invalid amount of gems - fixes #8145 (#8688)

* Translation string for error notification

* Use function instead of a link for paypal

* Inject notification service, function to check the amount of gems to purchase, function to handle payments with paypal

* Throw error if amount of gems is zero or negative

* Add condition to raise error if amount is negative

* Added gem errors for gifts 0 or less

* Fixed linting and broken test

* Fixed test syntax

* Added back needed strings

* Fixed group locales

website/server/libs/stripePayments.js

@@ -107,6 +107,9 @@ api.checkout = async function checkout (options, stripeInc) {
       if (gift.type === 'subscription') {
         amount = `${shared.content.subscriptionBlocks[gift.subscription.key].price * 100}`;
       } else {
+        if (gift.gems.amount <= 0) {
+          throw new BadRequest(shared.i18n.t('badAmountOfGemsToPurchase'));
+        }
         amount = `${gift.gems.amount / 4 * 100}`;
       }
     }