Added screen repository interrupts constant

Necessary to define -- via a single constant and object -- the kinds of screens that are interrupts.

Milestone: minor

app/repositories/screen.rb

@@ -4,6 +4,8 @@ module Terminus
   module Repositories
     # The screen repository.
     class Screen < DB::Repository[:screen]
+      INTERRUPTS = %w[error notification sleep wake welcome].freeze
+
       commands :create
 
       commands update: :by_pk,