ssh: use fingerprint when deleting public keys

Avoid relying on a database index of the full public key string.

ssh: keep track of latest use of SSH keys

Based on work by Ilya Beda <ir4y.ix@gmail.com> on
https://bitbucket.org/ir4y/rhodecode/commits/branch/ssh_server_support , also
heavily modified by Mads Kiilerich.

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.