repo-review: Add set/delete topic and set hashtags

Test: ./repo_review.py --set-topic test [query]
Test: ./repo_review.py --delete-topic [query]
Test: ./repo_review.py --add-hashtag test [query]
Test: ./repo_review.py --remove-hashtag test [query]
Change-Id: Ie7a1b82022d81850754543366202892c437f7968