added custom data parameter when a user joins to a meeting

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

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

...b/src/java/org/bigbluebutton/api/ParamsProcessorUtil.java

...on-web/src/java/org/bigbluebutton/api/domain/Meeting.java