Add a whole bunch of new ve.track() events for instrumenting loading and saving

Renamed events:
* performance.domLoad --> performance.system.domLoad
* performance.domSave --> performance.system.domSave

New events:
* performance.system.activation: total load time
* performance.system.domDiff: timing of paction=diff; like .domSave
* performance.system.domSerialize: timing of paction=serialize; like .domSave
* behavior.lastTransactionTillSaveDialogOpen: time from last transaction
  until user opened save dialog
* behavior.saveDialogOpenTillSave: time from save dialog opening to user
  clicking save
* behavior.saveDialogOpenTillReview: time from save dialog opening to user
  clicking review (skipped when a cached diff is shown)
* behavior.saveDialogClose: when user closes save dialog; duration is time
* performance.user.saveComplete: time from user clicking save to successful
  save completion; 'retries' indicates # of badtoken retries
* performance.user.saveError.*: time from user clicking save to failure;
  'retries' indicates # of badtoken retries
** performance.user.saveError.abusefilter
** performance.user.saveError.badtoken: token was bad and we prompted the user
** performance.user.saveError.captcha
** performance.user.saveError.editconflict
** performance.user.saveError.empty
** performance.user.saveError.spamblacklist
** performance.user.saveError.unknown
* performance.user.reviewComplete: time from user clicking review to diff showing
* performance.user.reviewError: time from user clicking review to diff failure
  since dialog was opened

Change-Id: I9815fa637d34c766c163e181d2f9527d3f32a7c3
(cherry picked from commit d6a00d689e41340d5737d1443e501243540b8c44)