Added Mark all in filter as read feature

Integrated feature
Added tests
In response to a users request(Issue #5113) i have added a feature that allows users to mark all notifications in the current notfication filter they're on as read without marking all the others read, i have also added tests for this feature in spec/controllers/notifications_controller_spec.rb
No need to pass an empty block. Also no need to re-declare the resource. Let's clean this whole block up to
```ruby
resource :notifications, :only => [:index, :update] do
  collection do
    get :read_all
    get :read_all_in_filter
  end
end
```