Calculator: improve triggers; add 'squared'

Some of the problems inherent in the old trigger regex made themselves
obvious once the 'squared' operation was added. This simplification
should make maintenance a smidge easier.

Resolves #482.
Calculator: improve superscript handling.

This fixes the problem of the simple case, but handling, say, expressions
in parens would require a lot more thought (a lexer would help!) I'll
leave that problem for another day.

Fixes #483.
Calculator: reset alarm when calculation is complete.

Total run time may well exceed 1 second with the pre- and post-
processing, but this makes it significantly less annoying to try things
out with `duckpan query`.

Also adds a test which shows the `duckpan query` parameters I was
trying, showing how `squared` is applied (and may result in confusion)
Calculator: style up the answer a bit.

This mostly just adds style to the HTML answers to be more in line with
other IAs.

The test changes are because, in general, the HTML answer is exactly the
same as the text answer, just wrapped up in some HTML. We're mostly
concerned with if we get correct answers, not how they happen to be
wrapped for HTML display.

In cases where that's different (the <sup> regression) we do more
thorough testing on the contents.

Also, removed one repeated test.

I'm starting to think this "apply_css" and maybe even "wrap_html" should
be in a role somewhere.
Merge pull request #488 from mwmiller/calc_updates

Calc updates