Refactor and update filtering

[jemus42]

See https://trakt.docs.apiary.io/#introduction/filters

Filters need to be updated to make available new filters like Rotten Tomatoes scores.
More importantly though, the way filters work should be refactored probably to dedicated helper functions like filters_shows() which can be documented and provide proper argument checks.
In relevant functions one would then pass a filters_show(...) object with corresponding defaults.

Filters should be more discoverable and easier to use, and this refactor would probably lead to a lot of deduplication.