Create test ApplicationContext through factory method.

Current version brings the concept of custom classes, which allows to define the concreate class that will be used to instantiate the ApplicationContext. Maybe it would be good idea to give the user full control on how the ApplicationContext will be created, so he can not only use some specialized implementation but would be also able to configure it correctly.

On the code level this would be achive by 'scaning' for static method that will be responsible for creating the ApplicationContext instance e.g.:

@SpringApplicationContext ApplicationContext [method_name]() {}