Create rake task that removes inactive / unused lists

[mshwery]

Need a disclaimer to tell people that empty lists will be removed after a certain time of inactivity.

class Stack
   has_many :lists
end

class List
   belongs_to :stack
end

use:

empty_stacks = Stack.includes(:lists).where( :lists => { :stack_id => nil } )
empty_stacks.map { |stack| stack.destroy }