DAR-254 Forum Activity Module refactor

This refactor fixes three bugs with the Forum Activity Module:

* A regression introduced by #785 that caused every minor edit to be displayed.
* If a thread listed in the module gets renamed, the title in module would not change.
* If a thread listed in the module gets removed, the thread would not disappear from the list.

Previously, this was doing up to five queries. I reduced it to one query that also also fixed the bugs above. It's still doing a full table scan because of a lack of indexes on certain columns. However, it was doing multiple full table scans before. So this is still an improvement. We will look into potentially adding indexes in the future.

The diff without whitespace is easier to read: https://github.com/Wikia/app/pull/982/files?w=1