Improve Screenshots

[wurzelkuchen]

It would be cool to have more details in the screenshots we provide for (failed) tests.

Possible screenshot enhancements:

• Mark the coordinates where the current click happened
• Mark the element which is currently used (for validation, click etc.)
• Allow Full site screenshot
• Think about marking the viewport in full site screenshots
• Highlight the current element/make additional screenshots only for the currently used elements
• ... anything else?

This however should be possible be configured/toggled via configuration.

[wurzelkuchen]

This is related to #11