There's no show action for ReadingsController

Signed off by: Guilherme Rojas V. de Lima <guilhermehrojas@gmail.com>
Refactored ReadingsGroupsController

set_reading_group on a before_action
ownership checkage semantically correct
Began to test concerns

Signed off by: Guilherme Rojas V. de Lima <guilhermehrojas@gmail.com>
Refactored readingGroup show

Splited Reading listing into two partials

Signed off by: Guilherme Rojas V. de Lima <guilhermehrojas@gmail.com>
Reviewd Reading model

Signed off by: Guilherme Rojas V. de Lima <guilhermehrojas@gmail.com>