Failing test to catch decorator inability to handle properties with interfaces

It turns out that decorator is creating a locator (in the `decorate` method) upfront without even checking if a property can be decorated or not. In particular case properties, whose `@var` annotation has as interface name won't be decorated.

This wasn't noticed until introduction of `WaitingElementLocator`, which searches for `@timeout` annotation in constructor, which results in attempt to introspect the interface from `@var` annotation of processed Page class property (see php-annotations/php-annotations#57).

This is semi-integration test to prove that described problem exists.