WebVTT Implementation Report Update

Hello,

I wanted to send an update on the WebVTT IR before the call this week so
that it can be reviewed ahead of time.

I've updated the wiki page [1] with a snapshot of the spreadsheet and a
description for each of the tests that do not have 2 passing
implementations. Every one of the failing tests is a browser implementation
bug and is fixable. None of these mean that the spec isn't implementable.

Thanks,
Gary.

[1] https://www.w3.org/wiki/TimedText/WebVTT_Implementation_Report