SUS-2050 | CategoryViewer: use CategoryRefreshCountsTask

[macbre]

https://wikia-inc.atlassian.net/browse/SUS-2050

Move heavy queries (and prone to database deadlocks) from Category::refreshCounts to an offline task.

[WikiaTech]

SonarQube analysis reported 25 issues

• 13 major
• 5 minor
• 7 info

Top 10 extra issues

Note: The following issues were found on lines that were not modified in the pull request. Because these issues can't be reported as line comments, they are summarized here:

1. Category.php#L30: Reduce the number of returns of this function 4, down to the maximum allowed 3.
2. Category.php#L191: Add curly braces around the nested statement(s).
3. Category.php#L256: Merge this if statement with the enclosing one.
4. CategoryViewer.php#L3: Add curly braces around the nested statement(s).
5. CategoryViewer.php#L6: Class "CategoryViewer" has 24 methods, which is greater than 20 authorized. Split it into smaller classes.
6. CategoryViewer.php#L100: Take the required action to fix the issue indicated by this "FIXME" comment.
7. CategoryViewer.php#L112: Replace this legacy wfMsg* function call with one of the new i18n functions.
8. CategoryViewer.php#L321: Extract this increment or decrement operator into a dedicated statement.
9. CategoryViewer.php#L378: Replace this legacy wfMsg* function call with one of the new i18n functions.
10. CategoryViewer.php#L396: Take the required action to fix the issue indicated by this "FIXME" comment.