Implemented capture screenshot on test failure

- feature is enabled by setting up property relativeScreenshotDirectory which point to directory where to store screenshots
- tests verify if screenshot is correctly created
Fix for multiplatform support - bcs. of WM is platform specific.
Fix compile time dependency bcs of platform WS specific.
Capture screenshot fixes:
- tycho support
- screenshots captured at the moment of failure, also in after and before
- fix default screenshots path
Update CaptureScreenshot.java