browser2: in debug, write html responses highlighting involved selectors

Browser2 HTML selectors tweak attributes of involved elements, then the
ItemElement writes an HTML file with the modified attributes and
restores the attributes.
This makes it easier to debug by showing visually for each object which
HTML elements were selected.
4 jobs for highlighting
Status Job ID Name Coverage
  Build
failed #460
build

 
  Test
skipped #461
lint
skipped #462
unittests
 
  Deploy
skipped #463
doc
 
Name Stage Failure
failed
build Build There is an unknown failure, please try again
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