Incomplete interface implementations

- [ ] `MSplashScreen.close` doesn't pass `force` kwarg defined on `IWindow.close`
- [ ] `MWindow` is missing `IWindow.key_pressed`
- [ ] `pyface.tests.test_new_toolkit.widget.Widget` doesn't fully implement the `IWidget` interface.
- [ ] `MEventTimer` doesn't fully implement the `ITimer` interface. It's missing a number of traits.
- [ ] `MCallbackTimer` doesn't fully implement the `ITimer` interface. It's missing a number of traits.
- [ ] null-backend `Widget` is missing the `show` method to fully implement `IWidget` interface.
- [ ] qt4 and wx-backend `DirectoryDialog.close` doesn't fully implement the `IWindow.close` interface - it's missing a `force` kwarg
- [ ] qt4 and wx-backend `Field` is missing the `show_context_menu` method to fully implement the `IField` interface.
- [ ] qt4 and wx-backend `FileDialog.close` doesn't fully implement `IWindow.close`. It's missing the `force` kwarg
- [ ] qt4-backend `HeadingText` is missing an `image` trait to fully implement the `IHeadingText` interface.
- [ ] qt4-backend `ProgressDialog` doesn't fully implement the `IDialog` interface - it is missing a number of traits and it doesn't fully implement `IWindow.close` as it's missing a `force` kwarg.
- [ ] qt4-backend `PythonEditor` is missing `set_style` to fully implement the `IPythonEditor`.
- [ ] qt4 and wx-backend `SingleChoiceDialog.close` is missing the `force` kwarg to fully implement `IWindow`
- [ ] qt4-backend `Window` is missing `key_pressed` to fully implement `IWindow`

See PR https://github.com/enthought/pyface/pull/554 which fixes all of these interface issues which seems to be causing test failures.