Add Action and Controller Attribute to applyLayout Tag Library

The attached patch adds the ability for a user of the applyLayout tag library to supply an action and controller to retrieve content from for use with SiteMesh. This eliminates the need to generate a URL for an action and controller (instead, the patch uses g:include). This change is really beneficial in a multi-plugin Grails application where one plugin needs to apply a layout via SiteMesh to content generated by an action and controller in another plugin.