Add stamp.io bitcoin hash publishing

[n8fr8]

Prove that you had this file and published it a certain time and place, using the blockchain.

http://docs.stampery.com/?shell#introduction

[elric-wamugu]

The service seems to be suspended for maintenance for an undefined time, since October 25, 2019. Source: https://telegra.ph/Stampery-Services-Currently-On-Maintenance-10-25

cc @n8fr8 @foundscapes

[foundscapes]

@hiromipaw we need to investigate to see if this is still relevant/useful

[hiromipaw]

@foundscapes I think we can investigate this via the filecoin research project?