move maven-script from Maven 2.2.x to maven-plugin-tools

maven-script, ie the ability to run plugins written with scripting languages like Ant and Beanshell, has been removed from Maven 3 core since it is an extension.
But it went nowhere: for the moment, it's only in Maven 2.2.x, see maven-script

IMHO, maven-plugin-tools would be a good home for these modules, which would contain plugin tools from build time to exec time