stbt.py: Incorrect first-pass "matched" text in match visualisation debug output
stbt.py: Incorrect first-pass "matched" text in match visualisation debug output

`stbt run -vv` and `stbt templatematch -v` output an html file in
`./stbt-debug/detect_match/*/index.html` to aid debugging of match
problems.

For the first-pass result, this file was saying "Matched" even when it
didn't match.

Note that the first-pass of the matching algorithm uses a "pyramid"
optimisation, where it operates on smaller versions (higher pyramid
levels) of the source & template images; only if a match is found does
it try the next larger version (lower level) of the images. Thus, if
there exists a lower level, it means that the higher level matched.
At the lowest level, we check `first_pass_matched`.

Really all of this information should be passed to
`_log_image_descriptions`, perhaps using the observer pattern, so that
`_log_image_descriptions` doesn't have to figure it out by inference.

Note also that the `levels` passed in to `jinja2.Template.render` is now
used more than once, so it has to be a list, not a lazy sequence.

stb-tester/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,wmanley/stb-tester,LewisHaley/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,wmanley/stb-tester,LewisHaley/stb-tester,wmanley/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester,martynjarvis/stb-tester,martynjarvis/stb-tester,wmanley/stb-tester,wmanley/stb-tester,martynjarvis/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester