Remove Groovy jars duplication in generated project

Generated sample Groovy project uses groovy.jar (core) while some
dependencies (like Spock) have groovy-all.jar as a transitive
dependency. Gradle treats them as different libraries and there is
a warning about duplicated classes (like AST transformations) during
compilation.
This commit adds global (for all configurations) rule to replace all
modularized Groovy jars with groovy-all artifact.
Merge pull request #254 from szpak/topic/duplicatedGroovyJars

Remove Groovy jars duplication in generated project