Code review comment for lp:~adeuring/launchpad/bug-513382

OK, the five different images showing various combinations of red and grey heat icon are now in use.

I did not add the images to the huge sprite image because the images themselves carry information that is not represented anywhere else. This information would be lost if the heat icons are only used as background images.

I've added alt and title attributes, fixed one unrelated lint complaint (line too long) and removed a trailing whitespace.

A test of the bug heat view class needed some changes, as well as a page test helper function.

tests:

./bin/test -t bug-heat-view.txt
./bin/test -t xx-listing-basics.txt

no lint