Add a capability to tag another user in the comment box

[MaryConti]

Sometimes, you want a different person to look at something, or respond to a comment.  My team would like Collaborator to have a capability to tag another user.  For example, in Jira, you can use "@lastname,firstname" to tag another user.  We would like a similar capability in the comment boxes.

[mtalexan]

The effect of tagging a user would be equivalent to a poke, but would cite the review, file, and line number in the notification to them.

[OlegGontarenko]

Possibility to mention user by using '@' was implemented in Collaborator v.13.4. (shipped in December 2020)