Update FilterPaneService.groovy

Filter pane not working with Grails 2.4.2
org.codehaus.groovy.grails.compiler.GrailsClassLoader is deprecated we have to use 
org.codehaus.groovy.grails.compiler.injection.GrailsAwareClassLoader
Merge pull request #44 from sreekumarmn/patch-1

Update FilterPaneService.groovy