Explore and re-evaluate how grails-shell Scripts are provided to the application

[jamesfredley]

Issue description

There are many grails-shell Scripts commonly used while generating, maintaining and executing a Grails application. They are currently provided by profiles and plugins (default and non-default).

Some scripts are dependent on the plugin, where others are entirely standalone. Explore the best location for each script to live and how it is provided to the end application.

[jdaugherty]

Longer term, I think we need to recommend splitting the plugin code from the build/gradle code. This is the approach we took in grails-core and I don't see how this can work without this split. Otherwise, you're mixing code that uses different dependency sets and it will likely cause conflicts longer term.