current groovy version/scripts not compatible with java11

need to upgrade groovy scripts (also in richfaces-cdk repo) from 1.5 to 2.x compatibility

and update plugin from
```
<groupId>org.codehaus.groovy.maven</groupId>
<artifactId>gmaven-plugin</artifactId>
```
to
```
<groupId>org.codehaus.gmavenplus</groupId>
<artifactId>gmavenplus-plugin</artifactId>
```