another attempt to record videos only for failed tests

* Video is recorded to a temporary file and moved to the video folder,
  if the test failed. The same is done with 'before' screenshots.

* Properties simplified and refactored. Now it's possible to take video
  for whole test suite and take screenshots for failed tests.
Merge pull request #4 from papousek/videos-on-failure

another attempt to record videos only for failed tests