ssh keys publically available for sysadmins via http, the github way

Very helpful feature for sysadmins to get user ssh-keys and append in servers. For example:

http://github.com/devaroop.keys

After this merge, gitlab users will be able to use it the same way: 

    http://<gitlab_host>/<username>.keys

More information about its advantages: http://thechangelog.com/github-exposes-public-ssh-keys-for-its-users/

Duplicates: #5260 which is closed