Merge branch 'feature/3601'

Close #3601
Zend\Log\Logger::registerErrorHandler: Log previous exceptions and map severity of ErrorExceptions to priority + tests
Merge branch 'hotfix/ExceptionHandlerDoesntLogPreviousExceptions' of git://github.com/marc-mabe/zf2 into hotfix/3604
[#3604] CS and logic cleanup

- Extract common error priority map to static property
- Use descriptive names instead of abbreviations
Merge branch 'hotfix/3604' into develop

Forward port #3604

Conflicts:
	library/Zend/Log/Logger.php
	tests/ZendTest/Log/LoggerTest.php