Provide Class-Level Filtering

This uses [the periscope gem][periscope]. Define scopes and whitelist them to be accessed with Entry.periscope(hash_of_query_things).

[periscope]:https://rubygems.org/gems/periscope

QA Plan
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1. `rake db:setup db:seed`
2. `rails console`
3. `entry = Entry.first`
4. `results = Entry.periscoe(user: entry.user_id, actions: entry.action_type) && puts results.count`. You should see a random but large number of results.