PR #593 Adds default plan for deactivated account (fixes #431)

Issue #431 fixed.
In Preferences model add new field default_deactivated_plan_type_id which keep informations about which plan_type will be set up if user will be deactivated.
In Rails Admin in preferences there is a field which admin can set up.

Implicitly there is a plan_type with name "Closed" available in seed.rb file.