[IMSC] Action-379 HTML equivalents of the linePadding1 and multiRowAlign1 IMSC 1 tests

Action-379 [1] is to obtain PNGs to use as test criteria for the
linePadding1 and multiRowAlign1 tests in the IMSC 1 Implementation Report
[2].

[1] Action-379 https://www.w3.org/AudioVideo/TT/tracker/actions/379

[2] IMSC 1 Implementation Report
https://www.w3.org/wiki/TimedText/IMSC1_Implementation_Report


As part of the path to doing that I've created intermediate HTML versions,
attached. 

Please could you review and confirm that they do what you think they
should, from the test files?

If they do, any opinion on whether we should just use those as the test
criteria or generate a static PNG from them?

Notes:
* The multiRowAlign example uses the approach that Glenn has proposed for
the CSS mapping for TTML2 to support this functionality, i.e. specifying
inline-block display semantics for spans and using text-align.
* The fontSize is not set in the test file so I've used 6.7vh being
approximately the height of 1c using the initial cell resolution of 32 15.
* The fontFamily is not in the test file so I've used monospace,
sans-serif being the recommendation in TTML1SE for the initial value.

Kind regards,

Nigel