MOB-1141 New method in Latest Activity Api (P2 fix)

**DO NOT MERGE!**

This changes need to be reviewed by Mobile and Data/API teams. Then it should be QA'ed before pushing to production.

@SebastianMarzjan, can you code review it or ask anyone from your team to do it, please? :)

I added simple copy-tests in https://github.com/Wikia/api-tests/pull/30