Generate and display ssh public key fingerprints instead of key contents

Trello Card: https://trello.com/c/iB213gUS/8-show-individual-ssh-key-fingerprints-in-the-console

Updated files:
modified:   console/app/models/key.rb
modified:   console/app/views/settings/_keys.html.haml

Updated to generate ssh key fingerprint in the model, and display that fingerprint in the view instead of the content of the key
```Digest::MD5.hexdigest(Base64.decode64(content)).scan(/../).join(":")```