summary: Split code out of HTMLIndex

This patch moves the generation of the column headers out of the
HTMLIndex class and into a separate mako template.

This helps to simplify the HTMLIndex class, since this code included a
lot of special handling in that class.

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
templates/html/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 inherently
lazy); the second is that because it is a part of the Summary class, it
doesn't have to have the summary class passed to it, since it inherently
has access to ``self''.

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