Purchases: Implement Edit Payment Method page

[stephanethomas]

We should add a new page to allow users to edit the method of payment of an upgrade:

This new page should offer to:

• Update details of any stored credit card
• Associate any stored credit card to the current purchase (Purchases: Manage: Implement Use This Card feature #281)
• Delete any stored credit card not associated to any purchase
• Associate a new credit card to the current purchase (see Purchases: Manage: Implement Add a New Card page #280)

This following modal will be displayed when users click on any Use This Card button:

This following modal will be displayed when users click on any Delete Card button:

Here is the list of existing API endpoints that relate to this new page:

• https://public-api.wordpress.com/rest/v1/me/stored-cards
  Returns a list of credit cards stored during a previous payment
• https://public-api.wordpress.com/rest/v1/upgrades/:subscription_id/update-credit-card
  Updates the credit card data for a specific upgrade
• https://public-api.wordpress.com/rest/v1/me/stored-cards/:card_id/delete
  Deletes a specific stored credit card

[fabianapsimoes]

I'll close this for now. Payment Method Management will likely be a project for Gold in the future.

[drewblaisdell]

I opened #6721 to remove these components, as they are currently included in the build but not used anywhere. We can revert it when development on this feature starts again.