Unify uploaded presentation file naming across bigbluebutton-web.

...rs/org/bigbluebutton/web/controllers/ApiController.groovy

bigbluebutton-web/src/java/org/bigbluebutton/api/Util.java

...uebutton/presentation/PresentationUrlDownloadService.java

...g/bigbluebutton/presentation/SupportedDocumentFilter.java