Live HTML Performance Tests

This branch of ResearchLiveHTML adds timers for:
* building DOM
* applying HTML edits

These timers are *always* run. To see data use: Debug > Show Performance Data 

Looks for these operations:
* HTMLInstrumentation Build DOM
* HTMLDocument applyDOMEdits

For multiple runs, the data is displayed as: min/avg/max/last

@dangoor, @njx 
Is this the kind of tests we want? Or automated tests? Or both?