Summary.py: Move code out of HTMLIndex into a mako template

Moving the column headers out of the HTMLIndex class simplifies the
class, since the code that existed for handling this was special case.

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
templates/index_body.mako: remove unused subtestResult

This code was left over from an early iteration of the code, and isn't
used.

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
summary.py: Simplify the way HTMLIndex works

This patch replaces home-rolled code with built-in python functions,
this results in cleaner, simpler, and faster code.

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
Summary.py: Convert HTMLIndex class into a generator

This change does a couple of really nice things for us, first it cuts
down on the memory consumption by using a generator (which is lazy).
Further, as a part of the Summary.generate_html() method it doesn't need
to have the summary instance passed to it, reducing complexity.

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>