Use attributes rather than calling helper method

Signed-off-by: Michal Čihař <michal@cihar.com>
Rename filter for comments

We no longer distinguish source and target comments when translating.

Signed-off-by: Michal Čihař <michal@cihar.com>
Store comment counts in the database

Signed-off-by: Michal Čihař <michal@cihar.com>