Dashboard: Widget Edit "breaks" back button

## Expected Behavior

While editing a widget, I should be able to click the Back button in my browser to return to the Dashboard screen with my tabs.

## Current Behavior

When I edit a widget and click the back button, it returns me to the Dashboards list index page of all my Dashboards... essentially taking me to the "page before last"

## Possible Solution

During the editing of a Widget, if the User users the `Back` button functionality on their browser, we should capture it and handle it as a `Cancel` click.
If the User has made any modifications to the data before click Cancel or Back button, we should alert the user that their changes are about to be lost and give them an option to stop the process and save their work.