Create 'pay' page

[Klakurka]

Create 'pay' page:

Example: https://paybutton.org/pay/[bch_address]?amount=15?amount_type=USD

[Klakurka]

Although not a pre-req, it would be nice to have the server components setup to guarantee payment detection reliability as well as allow businesses to login and see/manage their payments.

[Klakurka]

We could also support an account ID, where we would then have the payment page show exactly the right themeing for that individual/company.

[Klakurka]

Superseded by PayButton/paybutton-server#136 on the server.