DefaultResolutionStrategy.copy() should copy componentSelectionRules, too.

- See https://github.com/gradle/gradle/pull/324
+review REVIEW-5137
Moved plugin development plugin to org.gradle.plugin.devel.plugins

+review REVIEW-4998
Changing extra info element name validation to fail earlier.

- Extracting validation into utility class
- Moving most validation test cases to XmlUtil unit test
+review REVIEW-5059