ve.EventSequencer: Post-event listening

modules/ve/ve.EventSequencer.js
* Class to sequence pre-event and post-event listening correctly

demos/ve/eventSequencer.html
* Plain HTML example page for testing EventSequencer and event sequences

Change-Id: I4ddb10a30c2f44015136a7978a185d0b13f0690b
Merge "ve.EventSequencer: Post-event listening"