fix for http://jira.grails.org/browse/GPCONSOLE-9

I added a layout to the console's GSP to prevent it from using a default layout that may be defined in the application. I tested that this resolves the issue in an application that has the resources plugin installed.

I was concerned that if the plugin and host application both define a layout with the same name, that the application's layout might erroneously be used for the console page, so to minimise this risk I named the console's layout "console-plugin-layout.gsp".

I suspect this pull request might also fix GPCONSOLE-7.