Add configuration option to filter replies in lists (#9205)

* Add database support for list show-reply preferences

* Add backend support to read and update list-specific show_replies settings

* Add basic UI to set list replies setting

* Add specs for list replies policy

* Switch "cycling" reply policy link to a set of radio inputs

* Capitalize replies_policy strings

* Change radio button design to be consistent with that of the directory explorer

db/migrate/20181127165847_add_show_replies_to_lists.rb

@@ -0,0 +1,23 @@
+require Rails.root.join('lib', 'mastodon', 'migration_helpers')
+
+class AddShowRepliesToLists < ActiveRecord::Migration[5.2]
+  include Mastodon::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  def up
+    safety_assured do
+      add_column_with_default(
+        :lists,
+        :replies_policy,
+        :integer,
+        allow_null: false,
+        default: 0
+      )
+    end
+  end
+
+  def down
+    remove_column :lists, :replies_policy
+  end
+end