[Core] Use Gherkin 6+ and Cucumber messages

[mpkorstanje]

Summary

• Implements the message formatter which will output cucumber messages as ndjson as well as an improved html formatter which renders a html report based on these messages.

• Switches the default parser to Gherkin 6+. This will enable rule support by default.

• The json formatter has been made optional and has been moved to gherkin-vintage. It does not support rules and will throw an exception when rules are used.

Types of changes

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).

Checklist:

• I've added tests for my code.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[coveralls]

Coverage increased (+1.5%) to 84.541% when pulling c50393c on gherkin8 into 4d98e02 on master.

[mpkorstanje]

Consideration: Add some maven checks to the build to ensure dependency convergence. We currently have allot of dependencies and transitive dependencies on messages. These should all be in sync. While the protobuf itself is forwards and backwards compatible, the bytecode is decidedly not.