Fix user tagging

[crablar]

Current experience:

• go here

• go to the comment and type "@" to start looking for a user; we have a large number of user accounts who do not have a first name + last name who have the name "Software Engineer"

• if you play around with the tagging interface, you will see that it does not appear in a consistent place throughout the page; also, the top search result gets highlighted even as you scroll down to other results

• we should not have any of the "Software Engineer" people in these search results

• the top result should not stay highlighted as you scroll down

• comment interface should render in a consistent place on the page every time

Please use Slack's @ tagging feature as a reference.

[marcosschlup]

@crablar do you think we can close this issue or do we leave those items for later?