An ability to mention user in code review comments.

As a user of forum I would like to have an ability to mention other users in code review comments via introduce [user] bb code and by using autocomplete (suggestion username list). If the name of user is found in system, after posting mentioned user should receive notification (if notifications are enabled in mentioned user's profile).
I need it for drawing other user’s attention to the certain fragment of code in code review.

Acceptance Criteria:

• introduce [user] bb code should work as described in JC-1428:
  • [user]username[/user] should become a link (default style: bold and underlined) to the user's profile;
  • Mentioned user should receive email notification. He should receive message even in the case he has no view/post/leave comments in code review/edit/ permissions for the branch;
  • Any user of forum should have an ability to disable email notifications via setting in Profile;
  • Username inside of [user] is case sensitive;
  • If there is no such nickname, then that username does not become a link - just a plain text ([user] should not be shown anyway);
  • If we edit some text, then mentioned people don't get notification again;
• suggestion username list should work as described in JC-1395:
  • suggestion username list is shown if user enters "@" and a symbol of username. “@” must be the first symbol in the code review comment or must follow a space.
  • after choosing a username from list of users, it becomes a [user]username[/user] bb code;
  • search is case-insensitive;
  • if there is no such nickname, then it's just a simple text with @ on the beginning;
  • if there is several names match criteria, first 10 names will be shown in the list;
  • user can move the focus in the list via arrows button; close the list via Esc button; accept name via Enter;
• Notification templates:
  EN: You were mentioned in comment to code review "here we must put link to comment".
  RU: Вы были упомянуты в комментарии к рецензии кода "здесь нужно указать ссылку на комментарий".
  UK: Вас згадали в коментарі до рецензії коду: "тут потрібно вказати посилання на коментар".