Display users' status messages on the user handle in markdown
### Problem to solve
Users are mentioned in several places across GitLab which might mean that they've been effectively ping-ed when, in fact, they're OOO for 2 weeks.
### Intended users
Everyone who uses: Issues, Epics, MRs and also gets involved in discussions anywhere.
### Further details
This will prevent communication breakdown and expectation failures by improving visibility of users' availability.
### Proposal
<img src="/uploads/285860edc803f35b4ed7a05c98d76e91/Screen_Shot_2019-03-20_at_11.42.53.png" width="300">
Which on hover will display the popover, which will clarify what the user status is.
<img src="/uploads/5b54e2d28118e24a363c18ec4571b790/Screen_Shot_2019-03-20_at_11.42.59.png" width="400">
### What does success look like, and how can we measure that?
A good scenario to test is when pinging users for QA issues, which have a very short deadline, we can clearly see which are the users that might not be available in time by checking usernames with emojis in front.
### Links / references
issue