Move some controller logic into controller helpers that can be included ...

...in extensions
This should allow extensions to add authentication by simply including the required module

Note that `Include Monologue::ControllerHelpers::Auth` depdends on `Include Monologue::ControllerHelpers::User`. There might be a way with `ActiveSupport::Concern` to resolve this dependency but I am not sure how exactly. 
@jipiboily. If you know how, please feedback :)