Event Logger: collect IME functionality info

ve/ce/SurfaceObserver.js
* Do not setTimeout if frequency === null

demos/ve/eventLogger.html
* Standalone event logging script

ve/test/ce/imetests/*.js
* JSON event logs for various tests/browsers/IMEs

ve/test/ce/ve.ce.test.js
* Add an IME test

VisualEditor.hooks.php
* Add test files

Change-Id: I50e89d5a289f3fcb4fe2a6835a2ec96fb497242c