Adding exclusive lists feature

Major new feature, currently testing in a branch right now. Fixes #1

db/migrate/20190726034905_add_is_exclusive_to_lists.rb

@@ -0,0 +1,6 @@
+class AddIsExclusiveToLists < ActiveRecord::Migration[5.2]
+  def change
+    add_column :lists, :is_exclusive, :boolean
+    change_column_default :lists, :is_exclusive, false
+  end
+end