Merge pull request #3388 from jfederico/extension_preview_for_thumbnails_on_recordings

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

...vy/org/bigbluebutton/api/RecordingServiceHelperImp.groovy

...on-web/src/java/org/bigbluebutton/api/MeetingService.java

...-web/src/java/org/bigbluebutton/api/domain/Extension.java

...n-web/src/java/org/bigbluebutton/api/domain/Playback.java

...-web/src/java/org/bigbluebutton/api/domain/Recording.java

...ebutton-web/web-app/WEB-INF/freemarker/get-recordings.ftl

...ack/core/lib/recordandplayback/generators/presentation.rb

...and-playback/presentation/scripts/process/presentation.rb

...and-playback/presentation/scripts/publish/presentation.rb