CHG: unified getting a name of resource class
Squashed:

FIX: Fix for #218

REFACTOR: proc instead of if statement as suggested by @Daxter

FIX: syntax error

CHG: unified getting a name of resource class

CHG: There's no need to invoke ActiveSupport::Concern here. This version works just as well, with considerably less magic - help from Daxter

REFACTOR: Instead of passing "new_model" to translation_per_model, you should simply pass :new as an action, and then internally do this:

"#{action}_model"

I18n.t "active_admin.#{resource_class.to_s.downcase}.#{action}",
  :default => proc{ I18n.t "active_admin.#{action}_model", :model => model_label }
Note that this changes the behaviour quite a bit. That's because you shouldn't need to pass :model to the first translation, only to the default.

(suggestion from @Daxter)

ADD: form builder spec test
Merge branch '218-CLEAN-override-i18n-translations-for-specific-resources'

Conflicts:
	lib/active_admin/base_controller/translation.rb
	lib/active_admin/resource/action_items.rb