stbt batch report: Don't HTML escape files we read

Jinja will escape them when writing HTML out and we don't want them
double escaped.  We also want the ability to include HTML in notes.
fixup! WIP: report: Allow customising the columns
stbt batch report: Set table-layout: fixed

This allows us to set the width of columns to be less than the width of
their contents, required to be able to hide columns with `width: 0px`