Added ImportCustomizer.
 The customizer auto-imports commonly used types, packages and Level constants (incl. their lower-cased names as aliases)
LOGBACK-700: JMXConfigurator support in logback.groovy
Added jmxConfigurator method to ConfigurationDelegate which allows overriding the default context name or the entire ObjectName
Merge pull request #70 from jkuipers/groovy

LOGBACK-700 + ImportCustomizer for GafferConfigurator