[BC] Add jQuery plugin for Hashcash.io integration

This widget is an alternative to CAPTCHA-type of spam/brute-force
protection. It uses proof-of-work based on Dogecoin blockchain to make
sure user/bots do not run many tasks in parallel.

Trying to include npm auto update feature in this commit.

1GUnf2ZZRDS4BQJwv72BmrbpGc6MMogHya
Merge pull request #3494 from hippich/jquery.hashcash.io

[BC] [author] Add jQuery plugin for Hashcash.io integration