Add custom reporter

[dotnetprofessional]

To support livedoc reporting the model will need to be exported as a json file. Also the default mocha reporter doesn't represent the nature of Gherkin very well. As such a new visual reporter would be beneficial too.

Requirements:

• export full model including pass/fail/error etc to .json file
• provide a more Gherkin friendly text output

[dotnetprofessional]

livedoc now support both UI-Reporters aka Reporters in mocha and Post-Reporters which run after the UI-Reporter. This allows easier multi-reporter scenarios.