Implement Signup and invite

Created by: Tirokk

Authored by roschaefer Jun 23, 2019 Closed Jul 5, 2019

---

🍰 Pullrequest

Currently work in progress, but this PR should give us two features:

• Signup (disabled by a deployable configuration)
• Invite other users

Issues

• close #205 (closed)
• close #420 (closed)

Todo

• None