Multi-project Gradle Build

Key changes:
- Created top level build.gradle / settings.gradle
- Moved common tasks / definitions to gradle/java.gradle
- Added javadoc / source jar generation tasks
- Added maven plugin to install java (core / jetty-server) artifacts into mavenLocal()
- Added grails dependency on artifacts installed into mavelLocal()
- Replaced hard local dependencies with project references
- Upgraded gradle wrapper to version 1.2
- Tweaked eclipse project name generation to make them look hierarchical