Vmitnick/crema headlights

This logs an additional headlights event when assets are generated for a PSD where the user used Crema to set up generator, or for a PSD where the user didn't use generator, so we can compare the two.

To avoid having an even for every asset generated, I'm currently limiting it to a single one of each of these events per PS session, but might change that.
```document && (document !== undefined)``` is a little redundant. It's probably safer to just stick to ```if (document)``` just in case it's ```null``` as well.