remove deprecated CSV, sort_order, & namespace settings

Conflicts:
	lib/active_admin.rb
	lib/generators/active_admin/install/templates/active_admin.rb.erb
Change CSVBuilder to get column name from I18n

* Will try to get the column through Model.human_attribute_name.
* If the attribute name is not defined on the locale, the returned name will no longer be "titleized", it will be "humanized".
* If the value specified to the `column` method is not a symbol, it won't get the column name through I18n.
* Very useful when using locales. :)

Conflicts:
	lib/active_admin/csv_builder.rb
	spec/unit/csv_builder_spec.rb
Rename csv builder specs for better understanding

Conflicts:
	spec/unit/csv_builder_spec.rb
Delegate missing methods in CSV block to current view context

Conflicts:
	lib/active_admin/csv_builder.rb
	spec/unit/resource_spec.rb
Merge pull request #3038

Conflicts:
	app/views/active_admin/resource/index.csv.erb

Conflicts:
	app/views/active_admin/resource/index.csv.erb
	lib/active_admin/resource_controller/data_access.rb
don't use AS::Concern
move CSV building logic out of the controller

Conflicts:
	spec/unit/csv_builder_spec.rb