Make Drone CI configurable

app/models/setting.rb

@@ -51,6 +51,16 @@ class Setting < RailsSettings::Base
   field :discourse_connect_secret, type: :string,
     default: ENV["DISCOURSE_CONNECT_SECRET"].presence
 
+  #
+  # Drone CI
+  #
+
+  field :droneci_public_url, type: :string,
+    default: ENV["DRONECI_PUBLIC_URL"].presence
+
+  field :droneci_enabled, type: :boolean,
+    default: (ENV["DRONECI_PUBLIC_URL"].present?.to_s || false)
+
   #
   # ejabberd
   #