[#38] Wrote tests describing expected behavior of plugin

- Missing Identity Param In Event Causes Plugin To Yield Guest Identity
- Invalid Type In Event Identity Param Causes Plugin To Yield Guest Identity
- Valid Identity In Event Is Returned By Plugin
[#38] Implemented getIdentity() plugin

- Fixed test to use getMock() instead of getMockForAbstractClass();
  latter was always returning a clone of the event, while the former
  implemented the correct behavior (return the same instance).
- Plugin fully implemented to specs, and includes one additional test
  for if the controller implements the `InjectApplicationEventInterface`.
Update CS toolchain

- Use phpcs instead of php-cs-fixer
CS Fixes

- Per phpcs. Mostly long lines.
- Removed ModuleTest.php -- file was empty.
- Fixed case statements in AclAuthorizationFactoryTest; 2 were missing
  breaks!
[#38] Register getIdentity plugin with ControllerPluginManager

- Added configuration to register the getIdentity plugin.
[#38] Document plugin in README.
Merge branch 'feature/38'

Close #38