Add a testbed project for watchOS #275

What is the problem or limitation you are having?

There's not currently any way to (easily) test the operation of watchOS.

Describe the solution you'd like

The Python patch should be extended to include a testbed project for watchOS.

Describe alternatives you've considered

None

Additional context

watchOS projects are quite different to other platforms; however, it may be possible to crib a lot of content from the iOS testbed project.

It may also be worth investigating if a single testbed can be used for all Apple platforms, with multiple targets in a single project.