ssh: user management of ssh keys

Add user interface for managing SSH based access.

The work in this commit is based heavily off of the existing API key
code for the sake of consistency.

Updates to use Bootstrap, request.authuser, POST methods and pytest by Anton
Schur <tonich.sh@gmail.com>.

Additional Bootstrap fixes by Dominik Ruf.

The original code has been heavily modified by Mads Kiilerich.