webui: also show comments in problem view

Signed-off-by: Michal Toman <mtoman@redhat.com>
It is just sorting. It makes sure comments from different reports are included.
A very simple approach would be
```
result = []
for report in self.reports:
    result += report.comments
```
but that way if `problem.reports[0].comments` has more than `row_limit` comments, only comments from that single report would be shown. To avoid that, this results into
```
[problem.reports[0].comments[0],
 problem.reports[1].comments[0],
 problem.reports[2].comments[0],
 problem.reports[0].comments[1],
 problem.reports[1].comments[1]]
```