Add optional `view` argument to `Window.run()' and `arcade.run()`

[DragonMoffon]

To help promote subclassing views over the window itself, we should add an optional view argument to the run methods, letting them automatically call Window.show_view.

It results in only a one-line change, but it makes the DX (Developer Experice) nicer.

It will also need a unit test for each method, and the examples will need updating to take advantage of the change.