add jCenter() repository shortcut for Bintray's JCenter
Add jCenter repository for Aether
Update RepositoriesConfiguration.groovy

> "jcenter" a la Gradle
Update RepositoriesConfigurer.groovy

> "jcenter" a la Gradle
Update Ivy resolver tests for "jcenter" repo
Update Aether resolver for "jcenter"
Standardizing to "jcenter" in Ivy resolver
Standardizing to "jcenter" in Aether resolver
Merge branch 'master' of github.com:grails/grails-core
Merge branch 'master' of github.com:danveloper/grails-core
Merge pull request #437 from danveloper/master

add jCenter() repository shortcut for Bintray's JCenter