[LiveHTML] 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:
* HTMLInstr. Build DOM Full
* HTMLInstr. Build DOM Partial
* HTMLDocument applyDOMEdits

For multiple runs, the data is displayed as: min/avg/max/last

If you want to see array of times, you can click in tiny box in upper-right corner, press Ctrl+C to copy raw data, then paste it somewhere.

@dangoor, @njx 
Is this the kind of tests we want? Or automated tests? Or both?