Dunning polish, and multi-brand email template improvements

#On an invoice that's being dunned, show the actual dunning that is happening, with a link to the dunning path

For invoices that are having payments automatically retried (dunning), we've improved the notification so that you have a better view of both: 

1. What dunning actions/retries have taken place so far 
2. What the upcoming/next dunning actions are, and what day they will happen on

#Added support for making coupon codes taxable / non-taxable

We've added support for indicating that coupon codes are either taxable, or non-taxable (previously coupon codes were always non-taxable).

#Improved UI and multi-brand support for the From: field on email templates

We've improved the `From` addresses and `Subject` line boxes to allow you to more easily specify the `From` or `Subject` or an email template for customers using our `Brands` feature.

ChargeOver's `Brands` features are used to manage multiple businesses or brand-names from within a single ChargeOver account. Previously, it was difficult to specify a different email address or subject line per brand (for example, if you wanted to make the email address come from billing@company-ONE.com for one brand, and billing@company-TWO.com for the second brand).

We've made the boxes bigger and allowed merge tags in the box to make this easier:

#Added the ability to send invoices via USPS mail more than once

If you're using our `Print & Direct Mail` options to mail your hard-copy invoices via the United States Postal Service, we've added an option to let you mail the same invoice again (for example, in cases where the first copy was lost in the mail or lost by the customer). 

#Added more test credit cards for simulating different decline scenarios

We've added some new test credit card numbers that our developer community can use to simulate certain decline codes when building integrations with ChargeOver. Simulate declines due to invalid CVV codes, expired cards, insufficient funds, and more.

#REST API endpoints to delete usage/metered data

For developers using ChargeOver's metered data features (example: billing based on number of users, licenses, gigabytes of data used, etc.), we've added some new REST API endpoints to let you delete data points already posted to ChargeOver.

#When a subscription is cancelled, include the cancelled line items in the webhook payload

We've updated the webhook payload for cancelled subscriptions to include the line items on the subscription at the time of cancellation.

#REST API - add support for logging a user in to the customer portal and bouncing them specifically to the credit card add / update page

Log a user into the ChargeOver customer portal and automatically drop them on a specific page (example: immediately after logging in, put them on the "Update your payment method" page).

#Stripe - make sure we send the DESCRIPTION attribute when creating payment intents via the payment forms

Improved the Stripe integration so that when a customer pays for an invoice using a new credit card (that is, this is not an auto-pay subscription invoice), we send a Description note to Stripe with the associated ChargeOver invoice number.
Previously, ChargeOver sent this Description note to Stripe for automated payments or payments created by an admin of ChargeOver, but not when a customer paid themselves.

#ShipStation - if there is only a shipping charge, and no actual product, we do not include an ITEMS child XML node at all, which breaks ShipStation

Fixed a bug with the ShipStation integration which occurred when you created an invoice with only shipping charges on it. Previously, creating an invoice with only a shipping charge and no actual ship-able products broke the ShipStation integration. This has been fixed.