JSPWIKI-771:
- <pluginManagement/> must go inside <build/>
- default maven plugins have been put into <pluginManagement/>, to make the build independent of the maven version used
- enforcer plugin execution
   - JDK 6 required
   - Maven 3.0 or greater required
- sonar support
- moved common configuration from modules to parent pom
- javadoc generates a class/package UML diagram if it founds graphviz binary (www.graphviz.org) on path

git-svn-id: https://svn.apache.org/repos/asf/incubator/jspwiki/branches/MVN3_BRANCH@1469877 13f79535-47bb-0310-9956-ffa450edef68