More work with the InterlockingsController object; this time making it so we
 can display the number of assets that have been configured for a given
 interlocking. This details page also includes links to each of the asset
 type controllers to allow addition and editing of each asset type.

Next on the todo list for interlockings is to provide a form that allows the
 upload of .tag files or .csv descriptions of the channels. This will enable
 the auto-population of the channels table, providing something to set the
 asset object properties from.