UI: Inform user what meaning hourglass on reviews has

[6543]

as title - see screenshot

[codecov-commenter]

Codecov Report

Merging #12713 into master will increase coverage by 0.02%.
The diff coverage is 11.66%.

@@            Coverage Diff             @@
##           master   #12713      +/-   ##
==========================================
+ Coverage   43.29%   43.32%   +0.02%     
==========================================
  Files         646      646              
  Lines       71592    71567      -25     
==========================================
+ Hits        30993    31003      +10     
+ Misses      35583    35547      -36     
- Partials     5016     5017       +1     

Impacted Files	Coverage Δ
models/migrations/migrations.go	4.66% <ø> (ø)
models/migrations/v148.go	0.00% <0.00%> (ø)
models/user.go	53.56% <ø> (-0.20%)	⬇️
modules/graceful/server.go	47.00% <0.00%> (-0.41%)	⬇️
modules/highlight/highlight.go	24.69% <0.00%> (ø)
modules/migrations/gitlab.go	1.04% <0.00%> (-0.10%)	⬇️
modules/public/public.go	56.16% <0.00%> (ø)
modules/session/virtual.go	60.20% <0.00%> (ø)
routers/repo/issue.go	37.49% <0.00%> (-0.06%)	⬇️
modules/migrations/base/downloader.go	17.64% <5.12%> (-5.72%)	⬇️
... and 22 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e710a34...8d070c4. Read the comment docs.

[6543]

CI: Remote visit addressed rate limitation. :(