Stats - minor updates

Jan-Ivar reminded me of some things that needed updating.

You can see the diff I did here:

http://www.w3.org/2011/04/webrtc/wiki/index.php?title=Stats&diff=386&oldid=383

The most controversial (?) may be the addition of priority at both 
candidate and candidate pair level; given that the computation of the 
64-bit candidate pair priority is less simple than one would think, it 
seems to make sense to give both.