Normalize document.cookie

[antross]

Not sure what the best approach is here. Some ideas:

1. Recommend running with cookies disabled
2. Shim document.cookie to always return the empty string
3. Shim document.cookie to start as the empty string, but support writes

[antross]

Currently leaning toward a variation of idea 1 - run in private mode.

Note 1: the tracer extension must be explicitly allowed to run in private mode to still work.

Note 2: Edge and Firefox automatically isolate data between tabs, but Chrome shares data between tabs and requires fully exiting private mode before data is cleared.