Merge pull request #5338 from ritzalam/generate-png-images

.../main/java/org/bigbluebutton/presentation/PngCreator.java

...ton/presentation/imp/PdfToSwfSlidesGenerationService.java

...ava/org/bigbluebutton/presentation/imp/PngCreatorImp.java

bigbluebutton-web/grails-app/conf/UrlMappings.groovy

bigbluebutton-web/grails-app/conf/bigbluebutton.properties

bigbluebutton-web/grails-app/conf/spring/doc-conversion.xml

...gbluebutton/web/controllers/PresentationController.groovy

...org/bigbluebutton/web/services/PresentationService.groovy