skipping browser for patterns

[LarsHassler]

Functionality to define if a browser should be skipped for a specific pattern.

The problem I see here is, that the browsers are managed in the gemini config file and therefore have to live in two places, which is error-prone by design.
This could be handled in a way by reading in the gemini configuration and checking if the browser defined in the patternlab-to-gemini config is also present in the gemini config.

Not sure yet if this is a feature, that's worth implementing or not.