Add ability to retrieve resource name from the resource manager

Add ability to retrieve resource name from the resource manager The ResourceManager class provides methods to get version information and even create a new instance of a plugin based on the current request. However, the methods that help in getting the resource id (such as ::getMenuItem and getPageArguments) are protected. Since we are already able to get information on version, we should also be able to get the resource id using the resource manager class. This commit adds a method to do that. This blocks issue #939 where we need to get the resource plugin definition from an authentication plugin. Calling negotiate or trying to retrieve menu item information via menu_get_item results in an recursive call (infinite).