pkgsummary.py: Initial checkin for pkg summaries

This module collects package test results, and ultimately outputs a
JSON file for external consumption. Results can be at the section
or global level.

Test results are summarized by 'reporting-section' - a new
section-level config tag.

Targeted for DDPO integration of Piuparts results.
piuparts-report.py: Section-level summary support

If 'reporting-section'(s) are defined, output a 'summary.json' in the
section-level html directory.
pkgsummary.py: Add support for global merge

Add a JSON read function, and a summ merge function, with are needed
for merging the section summaries into a global summary.
piuparts-report.py: generate_global_summary()

At the end of processing, collect the section summary JSON files, and
consolidate the information into a single global JSON. Add a special
'overall' reporting-section, holding the 'worst' test result across
all of the ohter reporting-sections.
Add blocking count to the JSON summary format

It is zero for all but 'F'ailed records. Shows the numb4er of binary
packages which cannot be tested because of the failure. The number
used is the highest for all tests reflecting the source package and
reporting-section, regardless of which reporting-section url is
used.
pkgsummary.py: tooltip() routing for DDPO
changelog: Entry for summary.json
index.tpl: Placekeeper announce of summary.json

Document that there is a public interface available for piuparts
results.