All sibebar annotations' username is now a link to the users userstream

In the annotation template all user name is a link tag, with a href calculated by the new userLink filter.
Part of the solution for 523
Create directive for displaying the user name
Removed unused url field
Whitespace
Merge pull request #658 from hypothesis/523-link-user-names-to-user-streams-2

PR: Make all mentions of user names a link to the user stream