Update configuration for ActiveAdmin.

+ Command executed: `rails generate active_admin:install User`
+ For custom settings see 3883acd98f671029ebceab979096aa5f7da01863.
I18n alert message for unauthorized access to ActiveAdmin.
Update wording in ActiveAdmin specs.
Configure individual after_sign_path for superadmin and other users.
Allow editing for all Farm attributes.
Add Depot model to ActiveAdmin.