add utility to derive a seed from a password

MERGE REQUEST

Overview

Add a siac utility that allows you to derive a seed from a password. The password is hashed using blake2b and then the result is converted to a seed phrase. I needed this for personal reasons - I can now use my encryption passwords to recover my files + crypto - and since I had to write it anyway I figured I'd add it to siac.

Example for Visual changes (ie Screenshot)

Note that the password for this seed is 'a'

Issues Closed

Checklist

Review and complete the checklist to ensure that the MR is complete before assigned to an approver.

• All new methods, or updating methods have clear docstrings
• Testing added or updated for new methods
• Any new packages are added to Makefile and .gitlab-ci.yml
• API documentation updated for API updates
• Module README.md updated for changes to work flow
• Issue added to Sia-UI repo for new supporting features