Use FOP with grails

As there seem to be an error with the pom.xml for Apache FOP on maven central, just include the two offending avalon-framework packages beforehand (and we even use the newer versions, because org.apache.servicemix.bundles.fop does too).

dependencies {
    compile 'org.apache.avalon.framework:avalon-framework-api:4.3.1'
    compile 'org.apache.avalon.framework:avalon-framework-impl:4.3.1'
    compile('org.apache.xmlgraphics:fop:1.1') {
        excludes 'avalon-framework-api', 'avalon-framework-impl'
    }
}