take screenshot of whole website and crop afterwards
major refactor:
- changed filenames current/new -> failed pass
- always take screenshot of whole website
- define multiple elements per page without retake screenshot
enable all selector strategies for  elements
support selenium selector strategies for exclude attribute
removed unsupported attribute in README
removed obsolete test
several changes and fixes to make webdrivercss tests passing
fixed coverage test
updated README.md
improved test coverage by deleting obsolete code