Streamline the CSS3 animation tests for reliability

To make the CSS3 animation tests run more reliably:
- Separate the testing of 'onComplete' callback from the setting of
  CSS properties (currently incomplete, see TODO: messages)
- Avoid asynchronous asserts where possible (again, incomplete; may be
  able to eliminate the remaining ones with more work)
- Remove tests which became exact duplicates after doing the above
Merge pull request #169 from fmtvp/Css3AnimationTestsFix

Streamline the CSS3 animation tests for reliability