Pressing the browser "back" button or swiping backwards in the current MEX implementation does not function as expected for a good web browsing experience - the user agent is redirected to the previous URL (which might be a search page, another item, or a different website entirely).
Processes browser navigation events (presumably using the History API) to handle them in a meaningful way for the MEX UX.
Acceptance Criteria
- pressing / swiping back from a MEX modal closes the modal
- pressing / swiping back from the main item view navigates to the previous page in the browser
- the behaviour is covered by tests as far as possible.