[Page Visibility] Updated test suite

Hi All,



I submitted a bunch of changes to the Page Visibility test suite today.  Please take a look and let me know if you have any comments.

The key changes are:
- Updated the pagevisibilityharness file to be more consistent with the design of the Navigation Timing test suite.

- Deleted support files that were in the wrong directory.

- Updated some of the test names to be more clear on the test being performed.

- Fixed the links to the resources.

There are a couple of known issues:
- test_tab_state_change will not end early if the feature is not available and thus the callback does not occur.  It will only end after the timeout has elapsed.



- test_minimize has some stale implementation from the IE Testing Center and needs to be updated to match our suite.  This will need to happen in a future drop.



Thanks,

Karen