Now able to specify name of TestDataConfiguration file in Config.groovy

When having a project with multiple inlined plugins one gets an "Invalid duplicate class definition of class TestDataConfig", if the TestDataConfig.groovy file is present in multiple plugins depending on each other.
To solve this, I have changed the TestDataConfigurationHolder to read a setting in Config.groovy, and if grails.buildtestdata.testDataConfig is set, it will try to read this file instead of TestDataConfig.groovy.

Included is a small test project.