VisualEditor performance instrumentation: report counts

..so we can tell, for example, how many save attempts are made with a cache key.

Change-Id: I1c2a9d5bb199f9dea50b7d743bf9f8713ebc13ee
gdash: Strip (mw) and (cdn) prefixes from dashboard names

They don't add value, in my opinion.

Change-Id: Ia9f879644b901e71c433ca0befd94e5da5f54b1a