[SPARK-2299] Consolidate various stageIdTo* hash maps in JobProgressListener

This should reduce memory usage for the web ui as well as slightly increase its speed in draining the UI event queue. 

@andrewor14
Note that I dropped activeTime here (time taken for currently active tasks) because I'm not sure if the extra data structure required to track this is worth the benefit (I don't know if anybody really looks at this ...)