Filter stats announcements in admin by title/slug

www.agileplannerapp.com/boards/173808/cards/5170

this is just a first-pass at getting a search and
filter interface in place for stats announcements.
editors have an immediate need to start searching
by title and slug, so we put in place that first.
you are right @tekin about the nature of these tests. that's the style which has been adopted here for writing controller tests, so i was not to keen on breaking the convention. also, there are a limited set of cucumber tests, so i'm assuming we want to test only critical user flows in cucumber. i'm adding a test to ensure that the correct stats announcement is assigned to `@statistics_announcements` used for rendering the template.