(bug): Periods break the @ tag so tagging users with periods in their usernames is impossible.

Summary

Periods break the @ tag so tagging users with periods in their usernames is impossible.

Steps to reproduce

1. Visit your channel
2. Type "@thefreethoughtproject.com" in a comment on one of your posts and hit enter.

Additional commentary in Asana: https://app.asana.com/0/621013995005190/793533299158050

Platform information

Chrome/Win10

What is the current bug behavior?

The period breaks the @ tag so tagging users with periods in their usernames is impossible.

What is the expected correct behavior?

Either usernames with periods should not be allowed (and all current usernames with periods should have periods removed from their usernames) or users should be able to tag usernames with periods in them. I suggest the latter.

Relevant logs and/or screenshots

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)