[serialization] Layout for when `write` test results are available

[izzyreal]

Maybe I could do some preliminary work on integrating write test results. If the prospective API is already known, that would be nice to have, but much of the other requirements can already be taken care of.

What kind of layout do you have in mind?

Some ideas:

1. Make it one big page where the current content is repeated once below it, populated with write results. Both content chunks would have a header. Simple UI change but lots of scrolling required for those who want to see write.
2. Same layout as now, but with a button to toggle between read and write view.
3. A 3-state toggle or radio button for read only, write only, read and write views.

We may want to anticipate if the current sorting by name would work out favorably, and yields easily identifiable pairs on the screen for tests where both both read and write tests exists. If it is indeed valuable to be aware of such pairs, we may even want to think about visual emphasis, like giving the testname fields a distinct background color.

Update: ideas 1. and 2. are off the table because @GreyCat already mentioned separate and aggregated view for reading and writing tests on Gitter.