Update to Maze Runner v8

[twometresteve]

Goal

Upgrade e2e tests to Maze Runner v8.

Design

Whilst preparing this change, BrowserStack removed support for Appium 1.8.0. I've worked round that by changing the test fixture to poll for Maze commands rather than react to button presses (which cause instability on iOS 10/11 with the version of Appium that we now have access to). I've refactored the code for polling for commands into a new Thread class.

Changeset

Scenarios also updated in line with the Maze Runner upgrade guide.

Testing

Covered by a full CI run.

[github-actions]

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