Working on the feed item model tests
[#67318904] Finish FeedItem model tests

Also includes:
- a new FeedItemsController test (10 most recent feed items)
- a new scope on FeedItem (most_recent)
- updates to satisfy the linter
Merge pull request #8 from cloudspace/67318904_write_tests_for_the_feed_item_model

Tests for the feed item model