Proof parsing & GitHub proof

[biern]

This grew larger than intended. Closes #35 Closes #36 Closes #31

• I've created a github account for the purposes of E2E testing with a sample valid proof: https://github.com/foobar32167 You can test it by loading a acc2.txt fixture. I didn't want the username to be in any way affiliated with signhash to avoid phishing attempts, hence the random name.
• The implemented proof template is just a draft. Let's keep the discussion on how should it exactly be worded in a separate issue.
• Proof parsing errors are displayed in their raw form, I've created another issue to enhance that #40

[biern]

Also, I've created the https://github.com/SignHash/signhash-proof-template repo for the reference proof. It can be directly imported from the github UI when creating a new repo for ones proof. This allows to have a valid proof setup using only GitHub UI, without even touching the git cli.