POC Create and Monitor a Purchase

Description

This will demonstrate it is possible to create a purchase and send it to a seller's node from inside a browser client.

The POC can have a hard-coded buyer key it uses for signing, or it can derive that key from a seed as in #4

[ ] There should be an input field for the url to a listing. The listing doesn't need to be shown, all that is needed is the ability to enter a listing to be purchased.
[ ] When a purchase button is clicked, the data for the listing in the listing input will be loaded and used to send a purchase message to a messaging server (see #3).
[ ] The purchase message will need to be signed with the buyer's key.
QUESTION: What other data is needed to create multisig transactions for offline and moderated purchases?

[ ] When a purchase is created, it should be possible to pay for it with an external wallet.
[ ] A payment address will need to be created and displayed, along with a payment amount.

[ ] Once a payment is made, it should be monitored for confirmation.
- This will require the UXTOs, they should be available when the payment information is created?
- It is ok to use a standard blockchain explorer for this, unless OB1 insight servers are ready for use.
[ ] Once the payment is confirmed, a confirmation message should be displayed on-screen.