Navigating between explore and report page with back button does not work

A common thing I do is to write some code in the "explore" mode, and check on the "report" mode occasionally. My first reaction to go from the report mode back into explore is to hit the back button, which navigates back to the previous page (not the explore view).

### What I Did

1. Start at https://alpha.iodide.io/ (the homepage)
2. Click on "A Brief Tour through Iodide" (or any other notebook)
3. Click on "REPORT" in the top right
4. Click browser back button

### What I Expected

I expect the page to navigate back to "EXPLORE", which is the last immediate view. An alternative is to provide the same dialog when "backspace" is pressed.

### What Happened

I navigate back to the homepage without warning dialog, losing any computed state. This is particularly felt when running python-heavy notebooks.