bip21: support bitcoin uri scheme

[lvaccaro]

update uri interface to support bip23 uri as: /bitcoin/bitcoin:<address>?amount=<decimal>&label=<text> .

• update webserver interface
• add bip21 struct + serialization/deserialization with url encoding
• add new section to html page if specified in the bip21 as the following image

[notmandatory]

ACK 9113c10 . Nice improvement! I verified the QR Code displayed and the URI expected match. Also tested that going to URL:

http://0.0.0.0:8080/bitcoin?amount=10&label=test%20test

redirects to the expected next unused address URL:

http://0.0.0.0:8080/bitcoin/bitcoin:tb1q32a23q6u3yy89l8svrt80a54h06qvn7gnuvsen?amount=10&label=test%20test

I also verified on my test heroku app:

https://steves-btcts.herokuapp.com/bitcoin/bitcoin:tb1q32a23q6u3yy89l8svrt80a54h06qvn7gnuvsen?label=test&amount=10

[lvaccaro]

refactored in #36