Providing fallback configuration.

* Refactoring package structure;
* Defining Assertable behaviors in interfaces;
* Moving classes to internal package;
* Providing access to internal package members through factory;
Added fallback to DefaultProcessAssertConfiguration.

* Updated example tests to re-use test configuration;
* Added ProcessEngineListener to configuration to de-register services
on ProcessEngine close;
* Added lazy-loading of EngineServices if not provided in configuration
to minimize need for active configuration.