stbt batch report: Use table-layout:fixed

This fixes a variety of issues with the table display:

* On narrow windows, or with lots of extra-columns, the table used to exceed the width of its parent div. Once you clicked on a row, the right-hand pane would hide the overflowing part of the table so you wouldn't be able to see those columns.
* Table cell contents no longer wrap, so each table row is the same height, and you can fit in more rows per screen.
*  Since we're using CSS for the table-cell truncation we can include the full failure-reason and notes in the html, which means that the client-side search/filtering works on those fields.

Performance-wise I had hoped this would speed up rendering lots of results (10k+) but a while ago I had measured a similar change and it didn't have a noticeable effect.